HOME

TheInfoList




Spiders (
order Order or ORDER or Orders may refer to: * Orderliness Orderliness is associated with other qualities such as cleanliness Cleanliness is both the abstract state of being clean and free from germs, dirt, trash, or waste, and the habit of achieving a ...
Araneae) are air-breathing
arthropod An arthropod (, (gen. ποδός)) is an invertebrate Invertebrates are animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This includes all animals apart fr ...
s that have eight legs,
chelicerae The chelicerae () are the mouthparts of the Chelicerata, an arthropod An arthropod (, (gen. ποδός)) is an invertebrate animal having an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form ...

chelicerae
with fangs generally able to inject
venom Venom is a type of poison In biology, poisons are Chemical substance, substances that can cause death, injury or harm to organs, Tissue (biology), tissues, Cell (biology), cells, and DNA usually by chemical reactions or other activity (chemi ...

venom
, and
spinnerets A spinneret is a silk Silk is a natural fiber, natural protein fiber, some forms of which can be weaving, woven into textiles. The protein fiber of silk is composed mainly of fibroin and is produced by certain insect larvae to form coco ...

spinnerets
that extrude
silk Silk is a natural fiber, natural protein fiber, some forms of which can be weaving, woven into textiles. The protein fiber of silk is composed mainly of fibroin and is produced by certain insect larvae to form cocoon (silk), cocoons. The be ...

silk
. They are the largest order of
arachnid Arachnida () is a class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytica ...

arachnid
s and rank seventh in total species diversity among all
orders Orders is a surname In some cultures, a surname, family name, or last name is the portion of one's personal name that indicates their family, tribe or community. Practices vary by culture. The family name may be placed at either the start of ...
of organisms.Sebastin, P.A. & Peter, K.V. (eds.) (2009).
Spiders of India
'. Universities Press/
Orient Blackswan Orient Blackswan Pvt. Ltd. (formerly Orient Longman India, commonly referred to as Orient Longman), is an Indian publishing house headquartered in Hyderabad, Telangana. The company publishes academic, professional and general works as well as sc ...
.
Spiders are found worldwide on every continent except for
Antarctica Antarctica ( or ) is Earth's southernmost continent. It contains the geographic South Pole and is situated in the Antarctic region of the Southern Hemisphere, almost entirely south of the Antarctic Circle, and is surrounded by the Southern Oc ...

Antarctica
, and have become established in nearly every land
habitat Ibex in an alpine habitat In ecology Ecology (from el, οἶκος, "house" and el, -λογία, label=none, "study of") is the study of the relationships between living organisms, including humans, and their physical environment. ...

habitat
. , 49,623 spider
species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individu ...

species
in 129
families In human society, family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of families is to maintain the w ...
have been recorded by
taxonomists In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mecha ...
. However, there has been dissension within the
scientific community The scientific community is a diverse network of interacting scientist A scientist is a person who conducts scientific research The scientific method is an Empirical evidence, empirical method of acquiring knowledge that has characterize ...
as to how all these families should be classified, as evidenced by the over 20 different classifications that have been proposed since 1900. Anatomically, spiders (as with all arachnids) differ from other arthropods in that the usual body segments are fused into two tagmata, the
cephalothorax The cephalothorax, also called prosoma in some groups, is a tagma of various arthropod An arthropod (, (gen. ποδός)) is an invertebrate Invertebrates are animals that neither possess nor develop a vertebral column (commonly known as a ...
or prosoma, and the
opisthosoma The opisthosoma is the posterior part of the body in some arthropods, behind the prosoma (cephalothorax). It is a distinctive feature of the subphylum Chelicerata (arachnids, horseshoe crabs and others). Although it is similar in most respects to a ...
, or abdomen, and joined by a small, cylindrical
pedicel Pedicle or pedicel may refer to: Human anatomy *Pedicle of vertebral arch, the segment between the transverse process and the vertebral body, and is often used as a radiographic marker and entry point in vertebroplasty and kyphoplasty procedures * ...
, however, as there is currently neither paleontological nor embryological evidence that spiders ever had a separate thorax-like division, there exists an argument against the validity of the term cephalothorax, which means fused
cephalon Cephalon, Inc. was an American biopharmaceutical company co-founded in 1987 by pharmacologist Frank Baldino Jr., Frank Baldino, Jr., neuroscientist Michael Lewis, and organic chemist James C. Kauer—all three former scientists with the DuPont Co ...
(head) and the
thorax The thorax or chest is a part of the anatomy of humans, mammals, other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main Tagma (biology), divisions ...

thorax
. Similarly, arguments can be formed against use of the term abdomen, as the opisthosoma of all spiders contains a heart and respiratory organs, organs atypical of an abdomen. Unlike
insect Insects (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Rom ...

insect
s, spiders do not have
antennae Antenna (pl. antennas or antennae) may refer to: Science and engineering * Antenna (radio), also known as an aerial, a transducer designed to transmit or receive electromagnetic (e.g., TV or radio) waves * Antennae Galaxies, the name of two coll ...
. In all except the most primitive group, the
Mesothelae The Mesothelae are a suborder of spider Spiders ( order Araneae) are air-breathing arthropod An arthropod (, (gen. ποδός)) is an invertebrate animal having an exoskeleton, a Segmentation (biology), segmented body, and paired jointed a ...
, spiders have the most centralized nervous systems of all arthropods, as all their
ganglia A ganglion is a group of neuron cell bodies in the peripheral nervous system The peripheral nervous system (PNS) is one of two components that make up the nervous system In Biology, biology, the nervous system is a Complex system, high ...

ganglia
are fused into one mass in the cephalothorax. Unlike most arthropods, spiders have no
extensor Motion (physics), Motion, the process of movement, is described using specific anatomical terminology, anatomical terms. Motion includes movement of Organ (anatomy), organs, joints, limbs, and specific sections of the body. The terminology used d ...

extensor
muscles in their limbs and instead extend them by hydraulic pressure. Their abdomens bear appendages that have been modified into spinnerets that extrude silk from up to six types of glands.
Spider web A spider web, spiderweb, spider's web, or cobweb (from the archaic word '' coppe'', meaning "spider") is a structure created by a spider Spiders ( order Araneae) are air-breathing arthropod An arthropod (, (gen. ποδός)) is an inver ...

Spider web
s vary widely in size, shape and the amount of sticky thread used. It now appears that the spiral orb web may be one of the earliest forms, and spiders that produce tangled cobwebs are more abundant and diverse than
orb-weaver spider Orb-weaver spiders are members of the spider family (biology), family Araneidae. They are the most common group of builders of spiral wheel-shaped spider web, webs often found in gardens, fields, and forests. The English word ''orb'' can mean "cir ...
s. Spider-like
arachnid Arachnida () is a class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytica ...

arachnid
s with silk-producing
spigot A tap (also spigot or faucet: see usage variations) is a valve A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries A slurry composed of glass be ...
s appeared in the
Devonian The Devonian ( ) is a geologic period and system of the Paleozoic The Paleozoic (or Palaeozoic) Era ( ; from the Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the H ...
period Period may refer to: Common uses * Era, a length or span of time * Full stop (or period), a punctuation mark Arts, entertainment, and media * Period (music), a concept in musical composition * Period, a descriptor for a historical or period drama ...
about , but these animals apparently lacked spinnerets. True spiders have been found in
Carboniferous The Carboniferous ( ) is a geologic period The geologic time scale (GTS) is a system of chronological dating that classifies Geology, geological strata (stratigraphy) in time. It is used by geologists, paleontology, paleontologists, and other ...
rocks from , and are very similar to the most primitive surviving
suborder In biological classification, the order ( la, wikt:ordo#Latin, ordo) is # a taxonomic rank used in the classification of organisms and recognized by the nomenclature codes. The well-known ranks in descending order are: life, domain (biology), dom ...
, the
Mesothelae The Mesothelae are a suborder of spider Spiders ( order Araneae) are air-breathing arthropod An arthropod (, (gen. ποδός)) is an invertebrate animal having an exoskeleton, a Segmentation (biology), segmented body, and paired jointed a ...
. The main groups of modern spiders,
Mygalomorphae The Mygalomorphae, or mygalomorphs, are an infraorder In biological classification In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, che ...
and
Araneomorphae The Araneomorphae (also called the Labidognatha) are an infraorder In biological classification In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Bioch ...

Araneomorphae
, first appeared in the Triassic period, before . The species '''' was described as
herbivorous A herbivore is an animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular r ...
in 2008, but all other known species are
predator Predation is a biological interaction In ecology Ecology (from el, οἶκος, "house" and el, -λογία, label=none, "study of") is the study of the relationships between living organisms, including humans, and their physical env ...

predator
s, mostly preying on insects and on other spiders, although a few large species also take birds and lizards. It is estimated that the world's 25 million tons of spiders kill 400–800 million tons of prey per year. Spiders use a wide range of strategies to capture prey: trapping it in sticky webs,
lasso A lasso ( or ), also called lariat, riata, or reata (all from Castilian Castilian or Castillian may refer to: * Castile (historical region), Castile, a historic region of Spain ** Castilian people, an ethnic group from Castile ** Spanish ...

lasso
ing it with sticky
bolas A bolas (plural: ''bolas'' or ''bolases''; from Spanish ''bola'', "ball", also known as ''boleadoras'') is a type of throwing weapon A weapon, arm or armament is any implement or device that can be used with the intent to inflict damage or ...

bolas
, mimicking the prey to avoid detection, or running it down. Most detect prey mainly by sensing vibrations, but the active hunters have acute vision, and hunters of the
genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification In biology, taxonomy () is the scientific study of naming, defining (Circumscription (taxonomy), circumscribing) and classifying gr ...
''
Portia Thomson Financial was an arm of the Thomson Corporation, an information provider. When the Thomson Corporation merged with Reuters to form Thomson Reuters in April 2008, Thomson Financial was merged with the business of Reuters to form the Markets ...
'' show signs of intelligence in their choice of tactics and ability to develop new ones. Spiders' guts are too narrow to take solids, so they liquefy their food by flooding it with digestive
enzyme Enzymes () are protein Proteins are large s and s that comprise one or more long chains of . Proteins perform a vast array of functions within organisms, including , , , providing and , and from one location to another. Proteins diff ...

enzyme
s. They also grind food with the bases of their
pedipalp Pedipalps (commonly shortened to palps or palpi) are the second pair of appendage An appendage (or outgrowth) is an external body part, or natural prolongation, that protrudes from an organism In biology, an organism () is any orga ...
s, as arachnids do not have the mandibles that crustaceans and insects have. To avoid being eaten by the females, which are typically much larger, male spiders identify themselves to potential mates by a variety of complex
courtship Courtship is the period of development towards a sexual relationship An intimate relationship is an interpersonal relationship The concept of interpersonal relationship involves social associations, connections, or affiliations between ...

courtship
rituals. Males of most species survive a few matings, limited mainly by their short life spans. Females weave silk egg-cases, each of which may contain hundreds of eggs. Females of many species care for their young, for example by carrying them around or by sharing food with them. A minority of species are social, building communal webs that may house anywhere from a few to 50,000 individuals. Social behavior ranges from precarious toleration, as in the , to co-operative hunting and food-sharing. Although most spiders live for at most two years,
tarantula Tarantulas comprise a group of large and often hairy spiders of the family Theraphosidae. Currently, 1,010 species have been identified. The term "tarantula" is usually used to describe members of the family Theraphosidae, although many oth ...

tarantula
s and other
mygalomorph The Mygalomorphae, or mygalomorphs, are an infraorder of spiders, and comprise one of three major groups of living spiders with over 3000 species, found on all continents except Antarctica. Many members are known as trapdoor spiders due to the ...
spiders can live up to 25 years in captivity. While the venom of a few species is dangerous to humans, scientists are now researching the use of spider venom in medicine and as non-polluting
pesticide Pesticides are substances that are meant to control pest (organism), pests. The term pesticide includes all of the following: herbicide, insecticides (which may include insect growth regulators, termiticides, etc.) nematicide, molluscicide, pi ...
s. Spider silk provides a combination of lightness, strength and
elasticity Elasticity often refers to: *Elasticity (physics), continuum mechanics of bodies that deform reversibly under stress Elasticity may also refer to: Information technology * Elasticity (data store), the flexibility of the data model and the clu ...
that is superior to that of synthetic materials, and spider silk genes have been inserted into
mammal Mammals (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be i ...
s and
plant Plants are predominantly photosynthetic Photosynthesis is a process used by plants and other organisms to Energy transformation, convert light energy into chemical energy that, through cellular respiration, can later be released to fuel ...

plant
s to see if these can be used as silk factories. As a result of their wide range of behaviors, spiders have become common symbols in art and
mythology Myth is a folklore genre Folklore is the expressive body of culture shared by a particular group of people; it encompasses the tradition A tradition is a belief A belief is an Attitude (psychology), attitude that something is the ca ...

mythology
symbolizing various combinations of patience, cruelty and creative powers. An irrational fear of spiders is called
arachnophobia Arachnophobia is the intense and irrational fear of spider Spiders (order (biology), order Araneae) are air-breathing arthropods that have eight legs, chelicerae with fangs generally able to inject venom, and spinnerets that extrude spider s ...

arachnophobia
.


Etymology

The word ''spider'' derives from Proto-Germanic ''spin-þron-'', literally "spinner" (a reference to how spiders make their webs), from the Proto-Indo-European root ''*(s)pen-'', "to draw, stretch, spin".


Description


Body plan

Spiders are chelicerates and therefore
arthropod An arthropod (, (gen. ποδός)) is an invertebrate Invertebrates are animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This includes all animals apart fr ...
s. As arthropods they have: segmented bodies with jointed limbs, all covered in a
cuticle A cuticle (), or cuticula, is any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of "cuticle" are non-homology (biology), homologous, differing in the ...
made of
chitin units that repeat to form long chains in β-(1→4)-linkage. of the chitin molecule. Chitin ( carbon, C8H13O5N)n ( ) is a long-chain polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical su ...

chitin
and proteins; heads that are composed of several segments that fuse during the development of the
embryo An embryo is the early stage of development of a multicellular organism A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms ar ...

embryo
. Being chelicerates, their bodies consist of two tagmata, sets of segments that serve similar functions: the foremost one, called the
cephalothorax The cephalothorax, also called prosoma in some groups, is a tagma of various arthropod An arthropod (, (gen. ποδός)) is an invertebrate Invertebrates are animals that neither possess nor develop a vertebral column (commonly known as a ...
or
prosoma The cephalothorax, also called prosoma in some groups, is a Tagma (biology), tagma of various arthropods, comprising the head and the thorax fused together, as distinct from the abdomen behind. (The terms ''prosoma'' and ''opisthosoma'' are equiva ...
, is a complete fusion of the segments that in an
insect Insects (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Rom ...

insect
would form two separate tagmata, the
head Head Sport GmbH is an American-Austrian manufacturing company Manufacturing is the creation or production Production may be: Economics and business * Production (economics) * Production, the act of manufacturing goods * Production, in th ...

head
and
thorax The thorax or chest is a part of the anatomy of humans, mammals, other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main Tagma (biology), divisions ...

thorax
; the rear tagma is called the
abdomen The abdomen (colloquially called the belly, tummy, midriff or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. The abdomen is the front part of the abdominal segment of the Trunk (anatomy) ...

abdomen
or
opisthosoma The opisthosoma is the posterior part of the body in some arthropods, behind the prosoma (cephalothorax). It is a distinctive feature of the subphylum Chelicerata (arachnids, horseshoe crabs and others). Although it is similar in most respects to a ...
. In spiders, the cephalothorax and abdomen are connected by a small cylindrical section, the pedicel. The pattern of segment fusion that forms chelicerates' heads is unique among arthropods, and what would normally be the first head segment disappears at an early stage of development, so that chelicerates lack the
antennae Antenna (pl. antennas or antennae) may refer to: Science and engineering * Antenna (radio), also known as an aerial, a transducer designed to transmit or receive electromagnetic (e.g., TV or radio) waves * Antennae Galaxies, the name of two coll ...
typical of most arthropods. In fact, chelicerates' only
appendage An appendage (or outgrowth) is an external body part, or natural prolongation, that protrudes from an organism's body. In invertebrate biology, an appendage refers to any of the homology (biology), homologous body parts that may extend from a ...
s ahead of the mouth are a pair of
chelicerae The chelicerae () are the mouthparts of the Chelicerata, an arthropod An arthropod (, (gen. ποδός)) is an invertebrate animal having an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form ...

chelicerae
, and they lack anything that would function directly as "jaws". The first appendages behind the mouth are called
pedipalp Pedipalps (commonly shortened to palps or palpi) are the second pair of appendage An appendage (or outgrowth) is an external body part, or natural prolongation, that protrudes from an organism In biology, an organism () is any orga ...
s, and serve different functions within different groups of chelicerates. Spiders and
scorpion Scorpions are predatory Predation is a biological interaction In ecology Ecology (from el, οἶκος, "house" and el, -λογία, label=none, "study of") is the study of the relationships between living organisms, including hum ...

scorpion
s are members of one chelicerate group, the
arachnid Arachnida () is a class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytica ...

arachnid
s. Scorpions' chelicerae have three sections and are used in feeding. Spiders' chelicerae have two sections and terminate in
fang The four canines, or fangs, of a domestic cat. (The largest two teeth of the top and bottom rows of teeth.) A fang is a long, pointed tooth A tooth (plural teeth) is a hard, calcified structure found in the jaws (or mouths) of many vert ...

fang
s that are generally
venom Venom is a type of poison In biology, poisons are Chemical substance, substances that can cause death, injury or harm to organs, Tissue (biology), tissues, Cell (biology), cells, and DNA usually by chemical reactions or other activity (chemi ...

venom
ous, and fold away behind the upper sections while not in use. The upper sections generally have thick "beards" that filter solid lumps out of their food, as spiders can take only liquid food. Scorpions' pedipalps generally form large claws for capturing prey, while those of spiders are fairly small appendages whose bases also act as an extension of the mouth; in addition, those of male spiders have enlarged last sections used for
sperm Sperm is the male reproductive Cell (biology), cell, or gamete, in anisogamous forms of sexual reproduction (forms in which there is a larger, female reproductive cell and a smaller, male one). Animals produce motile sperm with a tail known as ...

sperm
transfer. In spiders, the cephalothorax and abdomen are joined by a small, cylindrical pedicel, which enables the abdomen to move independently when producing
silk Silk is a natural Nature, in the broadest sense, is the natural, physical, material world or universe The universe ( la, universus) is all of space and time and their contents, including planets, stars, galaxies, and all o ...

silk
. The upper surface of the cephalothorax is covered by a single,
convex Convex means curving outwards like a sphere, and is the opposite of concave. Convex or convexity may refer to: Science and technology * Convex lens A lens is a transmissive optics, optical device which focuses or disperses a light beam by me ...
carapace A carapace is a Dorsum (biology), dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tor ...
, while the underside is covered by two rather flat plates. The abdomen is soft and egg-shaped. It shows no sign of segmentation, except that the primitive
Mesothelae The Mesothelae are a suborder of spider Spiders ( order Araneae) are air-breathing arthropod An arthropod (, (gen. ποδός)) is an invertebrate animal having an exoskeleton, a Segmentation (biology), segmented body, and paired jointed a ...
, whose living members are the
Liphistiidae The spider family Liphistiidae, recognized by Tamerlan Thorell in 1869, comprises 8 genera and about 100 species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as w ...
, have segmented plates on the upper surface.


Circulation and respiration

Like other arthropods, spiders are
coelom The coelom (or celom) is the main body cavity A body cavity is any space or compartment, or potential space Potential generally refers to a currently unrealized ability. The term is used in a wide variety of fields, from physics to the social ...
ates in which the coelom is reduced to small areas around the reproductive and excretory systems. Its place is largely taken by a
hemocoel The circulatory system, also called the cardiovascular system or the vascular system, is an organ system that permits blood to circulate and transport nutrient A nutrient is a substance used by an organism to survive, grow, and reproduce. T ...
, a cavity that runs most of the length of the body and through which
blood Blood is a body fluid Body fluids, bodily fluids, or biofluids are liquid A liquid is a nearly incompressible In fluid mechanics or more generally continuum mechanics, incompressible flow (isochoric process, isochoric flow) refers t ...

blood
flows. The heart is a tube in the upper part of the body, with a few ostia that act as non-return valves allowing blood to enter the heart from the hemocoel but prevent it from leaving before it reaches the front end. However, in spiders, it occupies only the upper part of the abdomen, and blood is discharged into the hemocoel by one artery that opens at the rear end of the abdomen and by branching
arteries An artery (plural arteries) () is a blood vessel that takes blood away from the heart to one or more parts of the body (tissues, lungs, brain etc.). Most arteries carry oxygenated blood; the two exceptions are the pulmonary arteries, pulmonary ...

arteries
that pass through the pedicle and open into several parts of the cephalothorax. Hence spiders have open
circulatory system The circulatory system, also called the cardiovascular system or the vascular system, is an organ system An organ system is a biological system A biological system is a complex network Network and networking may refer to: Arts, entertai ...
s. The blood of many spiders that have
book lung A book lung is a type of respiration organ used for atmospheric gas exchange that is present in many arachnid Arachnida () is a class of joint-legged invertebrate Invertebrates are animals that neither possess nor develop a vertebral colum ...
s contains the
respiratory pigmentA respiratory pigment is a metalloprotein that serves a variety of important functions, its main being O2 transport. Other functions performed include O2 storage, CO2 transport, and transportation of substances other than respiratory gases. There ar ...
hemocyanin Hemocyanins (also spelled haemocyanins and abbreviated Hc) are proteins that transport oxygen throughout the bodies of some invertebrate animals. These metalloproteins contain two copper atoms that reversibly bind a single oxygen molecule (O2). ...
to make
oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

oxygen
transport more efficient. Spiders have developed several different respiratory anatomies, based on
book lung A book lung is a type of respiration organ used for atmospheric gas exchange that is present in many arachnid Arachnida () is a class of joint-legged invertebrate Invertebrates are animals that neither possess nor develop a vertebral colum ...
s, a
trachea The trachea, also known as the windpipe, is a cartilaginous Cartilage (cartilaginous tissue) is a resilient and smooth elastic tissue, rubber-like padding that covers and protects the ends of long bone A bone is a Stiffness, rigid tissue ...

trachea
l system, or both.
Mygalomorph The Mygalomorphae, or mygalomorphs, are an infraorder of spiders, and comprise one of three major groups of living spiders with over 3000 species, found on all continents except Antarctica. Many members are known as trapdoor spiders due to the ...
and
Mesothelae The Mesothelae are a suborder of spider Spiders ( order Araneae) are air-breathing arthropod An arthropod (, (gen. ποδός)) is an invertebrate animal having an exoskeleton, a Segmentation (biology), segmented body, and paired jointed a ...
spiders have two pairs of
book lung A book lung is a type of respiration organ used for atmospheric gas exchange that is present in many arachnid Arachnida () is a class of joint-legged invertebrate Invertebrates are animals that neither possess nor develop a vertebral colum ...
s filled with haemolymph, where openings on the
ventral Standard anatomical terms of location deal unambiguously with the of s, including s. Terms used generally derive from or roots and used to describe something in its . This position provides a definition of what is at the front ("anterior"), be ...

ventral
surface of the abdomen allow air to enter and diffuse
oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

oxygen
. This is also the case for some basal araneomorph spiders, like the family
Hypochilidae Lampshade spiders, family Hypochilidae, are among the most primitive of araneomorph spiders. There are two genus, genera and twelve species currently recognized. Like mygalomorphs, most hypochilids have two pairs of book lungs, but like araneomorp ...
, but the remaining members of this group have just the anterior pair of book lungs intact while the posterior pair of breathing organs are partly or fully modified into tracheae, through which oxygen is diffused into the haemolymph or directly to the tissue and organs. The tracheal system has most likely evolved in small ancestors to help resist
desiccation Desiccation (from Latin de- "thoroughly" + siccare "to dry") is the state of extreme dryness, or the process of extreme drying. A desiccant is a hygroscopic (attracts and holds water) substance that induces or sustains such a state in its lo ...
. The trachea were originally connected to the surroundings through a pair of openings called spiracles, but in the majority of spiders this pair of spiracles has fused into a single one in the middle, and moved backwards close to the
spinneret A spinneret is a silk Silk is a natural fiber, natural protein fiber, some forms of which can be weaving, woven into textiles. The protein fiber of silk is composed mainly of fibroin and is produced by certain insect larvae to form coc ...
s. Spiders that have tracheae generally have higher
metabolic rate Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main purposes of metabolism are: the conversion of the energy in food to energy available to run cell ...
s and better water conservation. Spiders are
ectotherm An ectotherm (from the Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population i ...
s, so environmental temperatures affect their activity.


Feeding, digestion and excretion

Uniquely among chelicerates, the final sections of spiders'
chelicerae The chelicerae () are the mouthparts of the Chelicerata, an arthropod An arthropod (, (gen. ποδός)) is an invertebrate animal having an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form ...

chelicerae
are fangs, and the great majority of spiders can use them to inject
venom Venom is a type of poison In biology, poisons are Chemical substance, substances that can cause death, injury or harm to organs, Tissue (biology), tissues, Cell (biology), cells, and DNA usually by chemical reactions or other activity (chemi ...

venom
into prey from venom
gland In animals, a gland is a group of cells in an animal's body that synthesizes substances (such as hormone A hormone (from the Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλά ...

gland
s in the roots of the chelicerae. The families
Uloboridae Uloboridae is a family In human society A society is a Social group, group of individuals involved in persistent Social relation, social interaction, or a large social group sharing the same spatial or social territory, typically subje ...
and Holarchaeidae, and some
Liphistiidae The spider family Liphistiidae, recognized by Tamerlan Thorell in 1869, comprises 8 genera and about 100 species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as w ...
spiders, have lost their venom glands, and kill their prey with silk instead. Like most
arachnid Arachnida () is a class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytica ...

arachnid
s, including
scorpion Scorpions are predatory Predation is a biological interaction In ecology Ecology (from el, οἶκος, "house" and el, -λογία, label=none, "study of") is the study of the relationships between living organisms, including hum ...

scorpion
s, spiders have a narrow gut that can only cope with liquid food and two sets of filters to keep solids out. They use one of two different systems of external digestion. Some pump digestive
enzyme Enzymes () are protein Proteins are large s and s that comprise one or more long chains of . Proteins perform a vast array of functions within organisms, including , , , providing and , and from one location to another. Proteins diff ...

enzyme
s from the midgut into the prey and then suck the liquified tissues of the prey into the gut, eventually leaving behind the empty husk of the prey. Others grind the prey to pulp using the chelicerae and the bases of the
pedipalp Pedipalps (commonly shortened to palps or palpi) are the second pair of appendage An appendage (or outgrowth) is an external body part, or natural prolongation, that protrudes from an organism In biology, an organism () is any orga ...
s, while flooding it with enzymes; in these species, the chelicerae and the bases of the pedipalps form a preoral cavity that holds the food they are processing. The stomach in the cephalothorax acts as a pump that sends the food deeper into the digestive system. The midgut bears many digestive , compartments with no other exit, that extract nutrients from the food; most are in the abdomen, which is dominated by the digestive system, but a few are found in the cephalothorax. Most spiders convert
nitrogen Nitrogen is the chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science ...

nitrogen
ous waste products into
uric acid Uric acid is a heterocyclic compound A heterocyclic compound or ring structure is a cyclic compound that has atoms of at least two different chemical element, elements as members of its ring(s). Heterocyclic chemistry is the branch of orga ...

uric acid
, which can be excreted as a dry material. Malphigian tubules ("little tubes") extract these wastes from the blood in the hemocoel and dump them into the
cloaca In animal anatomy, a cloaca (plural cloacae or ) is the posterior that serves as the only opening for the , reproductive, and s (if present) of many animals. All s, s, birds, and a few mammals (s, s, s, and s) have this orifice, from which ...
l chamber, from which they are expelled through the
anus The anus (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be in ...

anus
. Production of uric acid and its removal via Malphigian tubules are a water-conserving feature that has evolved independently in several
arthropod An arthropod (, (gen. ποδός)) is an invertebrate Invertebrates are animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This includes all animals apart fr ...
lineages that can live far away from water, for example the tubules of
insect Insects (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Rom ...

insect
s and arachnids develop from completely different parts of the
embryo An embryo is the early stage of development of a multicellular organism A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms ar ...

embryo
. However, a few primitive spiders, the sub
order Order, ORDER or Orders may refer to: * Orderliness Orderliness is a quality that is characterized by a person’s interest in keeping their surroundings and themselves well organized, and is associated with other qualities such as cleanliness a ...
Mesothelae The Mesothelae are a suborder of spider Spiders ( order Araneae) are air-breathing arthropod An arthropod (, (gen. ποδός)) is an invertebrate animal having an exoskeleton, a Segmentation (biology), segmented body, and paired jointed a ...
and infraorder
Mygalomorphae The Mygalomorphae, or mygalomorphs, are an infraorder In biological classification In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, che ...
, retain the ancestral arthropod
nephridia The nephridium (plural ''nephridia'') is an invertebrate Invertebrates are animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This includes all animals apart fr ...
("little
kidney The kidneys are two reddish-brown bean-shaped organs An organ is a group of tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's tissues can be broadly categorized ...

kidney
s"), which use large amounts of water to excrete nitrogenous waste products as
ammonia Ammonia is a chemical compound, compound of nitrogen and hydrogen with the chemical formula, formula NH3. A Binary compounds of hydrogen, stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct ch ...

ammonia
.


Central nervous system

The basic arthropod
central nervous system The central nervous system (CNS) is the part of the nervous system In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecu ...

central nervous system
consists of a pair of nerve cords running below the gut, with paired
ganglia A ganglion is a group of neuron cell bodies in the peripheral nervous system The peripheral nervous system (PNS) is one of two components that make up the nervous system In biology Biology is the natural science that studies li ...

ganglia
as local control centers in all segments; a brain formed by fusion of the ganglia for the head segments ahead of and behind the mouth, so that the
esophagus The esophagus (American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of varieties of the English language native to the United States. Currently, American E ...

esophagus
is encircled by this conglomeration of ganglia. Except for the primitive
Mesothelae The Mesothelae are a suborder of spider Spiders ( order Araneae) are air-breathing arthropod An arthropod (, (gen. ποδός)) is an invertebrate animal having an exoskeleton, a Segmentation (biology), segmented body, and paired jointed a ...
, of which the
Liphistiidae The spider family Liphistiidae, recognized by Tamerlan Thorell in 1869, comprises 8 genera and about 100 species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as w ...
are the sole surviving family, spiders have the much more centralized nervous system that is typical of arachnids: ''all'' the ganglia of all segments behind the esophagus are fused, so that the cephalothorax is largely filled with nervous tissue and there are no ganglia in the abdomen; in the Mesothelae, the ganglia of the abdomen and the rear part of the cephalothorax remain unfused. Despite the relatively small central nervous system, some spiders (like ''
Portia Thomson Financial was an arm of the Thomson Corporation, an information provider. When the Thomson Corporation merged with Reuters to form Thomson Reuters in April 2008, Thomson Financial was merged with the business of Reuters to form the Markets ...
'') exhibit complex behaviour, including the ability to use a trial-and-error approach.


Sense organs


Eyes

Spiders have primarily four pairs of eyes on the top-front area of the cephalothorax, arranged in patterns that vary from one family to another. The principal pair at the front are of the type called pigment-cup
ocelli A simple eye (sometimes called a pigment pit) refers to a form of eye Eyes are organs of the visual system The visual system comprises the sensory organ (the eye) and parts of the central nervous system (the retina containing photorecept ...
("little eyes"), which in most
arthropod An arthropod (, (gen. ποδός)) is an invertebrate Invertebrates are animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This includes all animals apart fr ...
s are only capable of detecting the direction from which light is coming, using the shadow cast by the walls of the cup. However, in spiders these eyes are capable of forming images. The other pairs, called secondary eyes, are thought to be derived from the
compound eye as imaged by an electron microscope A compound eye is a Eye, visual organ found in arthropods such as insects and crustaceans. It may consist of thousands of ommatidium, ommatidia, which are tiny independent photoreception units that consist of ...

compound eye
s of the ancestral chelicerates, but no longer have the separate facets typical of compound eyes. Unlike the principal eyes, in many spiders these secondary eyes detect light reflected from a reflective
tapetum lucidum The ''tapetum lucidum'' (; from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the ...
, and s can be spotted by torchlight reflected from the tapeta. On the other hand, the secondary eyes of jumping spiders have no tapeta. Other differences between the principal and secondary eyes are that the latter have rhabdomeres that point away from incoming light, just like in vertebrates, while the arrangement is the opposite in the former. The principal eyes are also the only ones with eye muscles, allowing them to move the retina. Having no muscles, the secondary eyes are immobile. The
visual acuity Visual acuity (VA) commonly refers to the clarity of vision Vision or The Vision may refer to: Perception Optical perception * Visual perception Visual perception is the ability to interpret the surrounding environment (biophysical), ...
of some jumping spiders exceeds by a factor of ten that of
dragonflies A dragonfly is a flying insect belonging to the order Odonata, infraorder Anisoptera (from Ancient Greek, Greek ἄνισος ''anisos'', "unequal" and πτερόν ''pteron'', "wing", because the hindwing is broader than the forewing). Adult d ...

dragonflies
, which have by far the best vision among
insect Insects (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Rom ...

insect
s. This acuity is achieved by a telephotographic series of lenses, a four-layer retina, and the ability to swivel the eyes and integrate images from different stages in the scan. The downside is that the scanning and integrating processes are relatively slow. There are spiders with a reduced number of eyes, the most common having six eyes (example, '' Periegops suterii'') with a pair of eyes absent on the anterior median line. Other species have four eyes and members of the Caponiidae family can have as few as two. List of troglobites, Cave dwelling species have no eyes, or possess vestigial eyes incapable of sight.


Other senses

As with other arthropods, spiders' Arthropod cuticle, cuticles would block out information about the outside world, except that they are penetrated by many sensors or connections from sensors to the nervous system. In fact, spiders and other arthropods have modified their cuticles into elaborate arrays of sensors. Various touch sensors, mostly bristles called setae, respond to different levels of force, from strong contact to very weak air currents. Chemical sensors provide equivalents of taste and Olfaction, smell, often by means of setae. An adult ''Araneus'' may have up to 1,000 such chemosensitive setae, most on the tarsi of the first pair of legs. Males have more chemosensitive bristles on their pedipalps than females. They have been shown to be responsive to sex pheromones produced by females, both contact and air-borne. The jumping spider ''Evarcha culicivora'' uses the scent of blood from mammals and other vertebrates, which is obtained by capturing blood-filled mosquitoes, to attract the opposite sex. Because they are able to tell the sexes apart, it is assumed the blood scent is mixed with pheromones. Spiders also have in the joints of their limbs slit sensillae that detect force and vibrations. In web-building spiders, all these mechanical and chemical sensors are more important than the eyes, while the eyes are most important to spiders that hunt actively. Like most arthropods, spiders lack balance and acceleration sensors and rely on their eyes to tell them which way is up. Arthropods' proprioceptors, sensors that report the force exerted by muscles and the degree of bending in the body and joints, are well-understood. On the other hand, little is known about what other internal sensors spiders or other arthropods may have.


Locomotion

Each of the eight legs of a spider consists of seven distinct parts. The part closest to and attaching the leg to the cephalothorax is the Arthropod leg#Coxa, coxa; the next segment is the short Arthropod leg#Trochanter, trochanter that works as a hinge for the following long segment, the Arthropod leg#Femur, femur; next is the spider's knee, the Arthropod leg#patella, patella, which acts as the hinge for the Arthropod leg#Tibia, tibia; the Arthropod leg#metatarsus, metatarsus is next, and it connects the tibia to the Arthropod leg#tarsus, tarsus (which may be thought of as a foot of sorts); the tarsus ends in a claw made up of either two or three points, depending on the family to which the spider belongs. Although all arthropods use muscles attached to the inside of the exoskeleton to flex their limbs, spiders and a few other groups still use hydraulic pressure to extend them, a system inherited from their pre-arthropod ancestors. The only
extensor Motion (physics), Motion, the process of movement, is described using specific anatomical terminology, anatomical terms. Motion includes movement of Organ (anatomy), organs, joints, limbs, and specific sections of the body. The terminology used d ...

extensor
muscles in spider legs are located in the three hip joints (bordering the coxa and the trochanter). As a result, a spider with a punctured
cephalothorax The cephalothorax, also called prosoma in some groups, is a tagma of various arthropod An arthropod (, (gen. ποδός)) is an invertebrate Invertebrates are animals that neither possess nor develop a vertebral column (commonly known as a ...
cannot extend its legs, and the legs of dead spiders curl up. Spiders can generate pressures up to eight times their resting level to extend their legs, and jumping spiders can jump up to 50 times their own length by suddenly increasing the blood pressure in the third or fourth pair of legs. Although larger spiders use hydraulics to straighten their legs, unlike smaller jumping spiders they depend on their flexor muscles to generate the propulsive force for their jumps. Most spiders that hunt actively, rather than relying on webs, have dense tufts of fine bristles between the paired claws at the tips of their legs. These tufts, known as scopulae, consist of bristles whose ends are split into as many as 1,000 branches, and enable spiders with scopulae to walk up vertical glass and upside down on ceilings. It appears that scopulae get their grip from contact with extremely thin layers of water on surfaces. Spiders, like most other
arachnid Arachnida () is a class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytica ...

arachnid
s, keep at least four legs on the surface while walking or running.


Silk production

The abdomen has no appendages except those that have been modified to form one to four (usually three) pairs of short, movable
spinneret A spinneret is a silk Silk is a natural fiber, natural protein fiber, some forms of which can be weaving, woven into textiles. The protein fiber of silk is composed mainly of fibroin and is produced by certain insect larvae to form coc ...
s, which emit
silk Silk is a natural fiber, natural protein fiber, some forms of which can be weaving, woven into textiles. The protein fiber of silk is composed mainly of fibroin and is produced by certain insect larvae to form cocoon (silk), cocoons. The be ...

silk
. Each spinneret has many
spigot A tap (also spigot or faucet: see usage variations) is a valve A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries A slurry composed of glass be ...
s, each of which is connected to one silk
gland In animals, a gland is a group of cells in an animal's body that synthesizes substances (such as hormone A hormone (from the Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλά ...

gland
. There are at least six types of silk gland, each producing a different type of silk. Silk is mainly composed of a protein very similar to that used in insect silk. It is initially a liquid, and hardens not by exposure to air but as a result of being drawn out, which changes the internal structure of the protein. It is similar in tensile strength to nylon and biological materials such as
chitin units that repeat to form long chains in β-(1→4)-linkage. of the chitin molecule. Chitin ( carbon, C8H13O5N)n ( ) is a long-chain polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical su ...

chitin
, collagen and cellulose, but is much more Deformation (engineering), elastic. In other words, it can stretch much further before breaking or losing shape. Some spiders have a cribellum, a modified spinneret with up to 40,000 spigots, each of which produces a single very fine fiber. The fibers are pulled out by the calamistrum, a comblike set of bristles on the jointed tip of the cribellum, and combined into a composite woolly thread that is very effective in snagging the bristles of insects. The earliest spiders had cribella, which produced the first silk capable of capturing insects, before spiders developed silk coated with sticky droplets. However, most modern groups of spiders have lost the cribellum. Even species that do not build webs to catch prey use silk in several ways: as wrappers for
sperm Sperm is the male reproductive Cell (biology), cell, or gamete, in anisogamous forms of sexual reproduction (forms in which there is a larger, female reproductive cell and a smaller, male one). Animals produce motile sperm with a tail known as ...

sperm
and for fertilized eggs; as a "Safety harness, safety rope"; for nest-building; and as "parachutes" by the young of some species.


Reproduction and life cycle

Spiders reproduce sexually and fertilization is internal fertilization, internal but indirect, in other words the
sperm Sperm is the male reproductive Cell (biology), cell, or gamete, in anisogamous forms of sexual reproduction (forms in which there is a larger, female reproductive cell and a smaller, male one). Animals produce motile sperm with a tail known as ...

sperm
is not inserted into the female's body by the male's genitals but by an intermediate stage. Unlike many land-living
arthropod An arthropod (, (gen. ποδός)) is an invertebrate Invertebrates are animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This includes all animals apart fr ...
s, male spiders do not produce ready-made spermatophores (packages of sperm), but spin small sperm webs onto which they ejaculate and then transfer the sperm to special syringe-styled structures, palpal bulbs or palpal organs, borne on the tips of the
pedipalp Pedipalps (commonly shortened to palps or palpi) are the second pair of appendage An appendage (or outgrowth) is an external body part, or natural prolongation, that protrudes from an organism In biology, an organism () is any orga ...
s of mature males. When a male detects signs of a female nearby he checks whether she is of the same species and whether she is ready to mate; for example in species that produce webs or "safety ropes", the male can identify the species and sex of these objects by "smell". Spiders generally use elaborate
courtship Courtship is the period of development towards a sexual relationship An intimate relationship is an interpersonal relationship The concept of interpersonal relationship involves social associations, connections, or affiliations between ...

courtship
rituals to prevent the large females from eating the small males before fertilization, except where the male is so much smaller that he is not worth eating. In web-weaving species, precise patterns of vibrations in the web are a major part of the rituals, while patterns of touches on the female's body are important in many spiders that hunt actively, and may "hypnotize" the female. Gestures and dances by the male are important for jumping spiders, which have excellent eyesight. If courtship is successful, the male injects his sperm from the palpal bulbs into the female via one or two openings on the underside of her abdomen. Female spiders' reproductive tracts are arranged in one of two ways. The ancestral arrangement ("haplogyne" or "non-entelegyne") consists of a single genital opening, leading to two seminal receptacles (spermathecae) in which females store sperm. In the more advanced arrangement ("entelegyne"), there are two further openings leading directly to the spermathecae, creating a "flow through" system rather than a "first-in first-out" one. Eggs are as a general rule only fertilized during oviposition when the stored sperm is released from its chamber, rather than in the ovarian cavity. A few exceptions exist, such as ''Parasteatoda tepidariorum''. In these species the female appears to be able to activate the dormant sperm before oviposition, allowing them to migrate to the ovarian cavity where fertilization occurs. The only known example of direct fertilization between male and female is an Israeli spider, ''Harpactea sadistica'', which has evolved traumatic insemination. In this species the male will penetrate its pedipalps through the female's body wall and inject his sperm directly into her ovaries, where the embryos inside the fertilized eggs will start to develop before being laid. Males of the
genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification In biology, taxonomy () is the scientific study of naming, defining (Circumscription (taxonomy), circumscribing) and classifying gr ...
''Tidarren'' amputate one of their palps before maturation and enter adult life with one palp only. The palps are 20% of the male's body mass in this species, and detaching one of the two improves mobility. In the Yemeni species ''Tidarren argo'', the remaining palp is then torn off by the female. The separated palp remains attached to the female's epigynum for about four hours and apparently continues to function independently. In the meantime, the female feeds on the palpless male. In over 60% of cases, the female of the Australian redback spider kills and eats the male after it inserts its second palp into the female's genital opening; in fact, the males co-operate by trying to impale themselves on the females' fangs. Observation shows that most male redbacks never get an opportunity to mate, and the "lucky" ones increase the likely number of offspring by ensuring that the females are well-fed. However, males of most species survive a few matings, limited mainly by their short life spans. Some even live for a while in their mates' webs. DirkvdM Nephila clavipes.jpg, The tiny male of the golden orb weaver (''Trichonephila clavipes'') (near the top of the leaf) is protected from the female by producing the right vibrations in the web, and may be too small to be worth eating. Orange spider egg sac.jpg, Orange spider egg sac hanging from ceiling Gasteracantha mammosa spiderlings next to their eggs capsule.jpg, ''Gasteracantha mammosa'' spiderlings next to their eggs capsule Lycosidae female carrying young.jpg, Wolf spider carrying its young on its abdomen Females lay up to 3,000 eggs in one or more silk egg sacs, which maintain a fairly constant humidity level. In some species, the females die afterwards, but females of other species protect the sacs by attaching them to their webs, hiding them in nests, carrying them in the
chelicerae The chelicerae () are the mouthparts of the Chelicerata, an arthropod An arthropod (, (gen. ποδός)) is an invertebrate animal having an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form ...

chelicerae
or attaching them to the
spinneret A spinneret is a silk Silk is a natural fiber, natural protein fiber, some forms of which can be weaving, woven into textiles. The protein fiber of silk is composed mainly of fibroin and is produced by certain insect larvae to form coc ...
s and dragging them along. Baby spiders pass all their larval stages inside the egg sac and emerge as spiderlings, very small and sexually immature but similar in shape to adults. Some spiders care for their young, for example a 's brood clings to rough bristles on the mother's back, and females of some species respond to the "begging" behaviour of their young by giving them their prey, provided it is no longer struggling, or even regurgitation (digestion), regurgitate food. Like other
arthropod An arthropod (, (gen. ποδός)) is an invertebrate Invertebrates are animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This includes all animals apart fr ...
s, spiders have to molt to grow as their
cuticle A cuticle (), or cuticula, is any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of "cuticle" are non-homology (biology), homologous, differing in the ...
("skin") cannot stretch.Ruppert, 523–24 In some species males mate with newly-molted females, which are too weak to be dangerous to the males. Most spiders live for only one to two years, although some
tarantula Tarantulas comprise a group of large and often hairy spiders of the family Theraphosidae. Currently, 1,010 species have been identified. The term "tarantula" is usually used to describe members of the family Theraphosidae, although many oth ...

tarantula
s can live in captivity for over 20 years, and an Australian female Ctenizidae, trapdoor spider was documented to have lived in the wild for 43 years, dying of a parasitic wasp attack.


Size

Spiders occur in a large range of sizes. The smallest, ''Patu digua'' from Colombia, are less than in body length. The largest and heaviest spiders occur among
tarantula Tarantulas comprise a group of large and often hairy spiders of the family Theraphosidae. Currently, 1,010 species have been identified. The term "tarantula" is usually used to describe members of the family Theraphosidae, although many oth ...

tarantula
s, which can have body lengths up to and leg spans up to .


Coloration

Only three classes of pigment (ommochromes, bilin (biochemistry), bilins and guanine) have been identified in spiders, although other pigments have been detected but not yet characterized. Melanins, carotenoids and pterins, very common in other animals, are apparently absent. In some species, the exocuticle of the legs and prosoma is modified by a Tanning (leather), tanning process, resulting in a brown coloration. Bilins are found, for example, in ''Micrommata virescens'', resulting in its green color. Guanine is responsible for the white markings of the European garden spider ''Araneus diadematus''. It is in many species accumulated in specialized cells called guanocytes. In genera such as ''Tetragnatha'', ''Leucauge'', ''Argyrodes'' or ''Theridiosoma'', guanine creates their silvery appearance. While guanine is originally an end-product of protein metabolism, its excretion can be blocked in spiders, leading to an increase in its storage. Structural coloration, Structural colors occur in some species, which are the result of the diffraction, scattering or interference of light, for example by modified setae or scales. The white prosoma of ''Argiope (spider), Argiope'' results from bristles reflecting the light, ''Lycosa'' and ''Josa (spider), Josa'' both have areas of modified cuticle that act as light reflectors. While in many spiders color is fixed throughout their lifespan, in some groups, color may be variable in response to environmental and internal conditions. Choice of prey may be able to alter the color of spiders. For example, the abdomen of ''Theridion grallator'' will become orange if the spider ingests certain species of Fly, Diptera and adult Lepidoptera, but if it consumes Homoptera or larval Lepidoptera, then the abdomen becomes green. Environmentally induced color changes may be morphological (occurring over several days) or physiological (occurring near instantly). Morphological changes require pigment synthesis and degradation. In contrast to this, physiological changes occur by changing the position of pigment-containing cells. An example of morphological color changes is background matching. ''Misumena vatia'' for instance can change its body color to match the substrate it lives on which makes it more difficult to be detected by prey. An example of physiological color change is observed in ''Cyrtophora cicatrosa'', which can change its body color from white to brown near instantly.


Ecology and behavior


Non-predatory feeding

Although spiders are generally regarded as predatory, the jumping spider '''' gets over 90% of its food from fairly solid plant material produced by acacias as part of a Mutualism (biology), mutually beneficial relationship with a species of ant. Juveniles of some spiders in the families Anyphaenidae, Corinnidae, Clubionidae, Thomisidae and Salticidae feed on plant nectar. Laboratory studies show that they do so deliberately and over extended periods, and periodically clean themselves while feeding. These spiders also prefer sugar solutions to plain water, which indicates that they are seeking nutrients. Since many spiders are nocturnal, the extent of nectar consumption by spiders may have been underestimated. Nectar contains amino acids, lipids, vitamins and minerals in addition to sugars, and studies have shown that other spider species live longer when nectar is available. Feeding on nectar avoids the risks of struggles with prey, and the costs of producing venom and digestive enzymes. Various species are known to feed on dead arthropods (scavenging), web silk, and their own shed exoskeletons. Pollen caught in webs may also be eaten, and studies have shown that young spiders have a better chance of survival if they have the opportunity to eat pollen. In captivity, several spider species are also known to feed on bananas, marmalade, milk, egg yolk and sausages.


Capturing prey

The best-known method of prey capture is by means of sticky webs. Varying placement of webs allows different species of spider to trap different insects in the same area, for example flat horizontal webs trap insects that fly up from vegetation underneath while flat vertical webs trap insects in horizontal flight. Web-building spiders have poor vision, but are extremely sensitive to vibrations. Females of the water spider ''Argyroneta aquatica'' build underwater "diving bell" webs that they fill with air and use for digesting prey, molting, mating and raising offspring. They live almost entirely within the bells, darting out to catch prey animals that touch the bell or the threads that anchor it. A few spiders use the surfaces of lakes and ponds as "webs", detecting trapped insects by the vibrations that these cause while struggling. Net-casting spiders weave only small webs, but then manipulate them to trap prey. Those of the genus ''Hyptiotes'' and the family Theridiosomatidae stretch their webs and then release them when prey strike them, but do not actively move their webs. Those of the family Deinopidae weave even smaller webs, hold them outstretched between their first two pairs of legs, and lunge and push the webs as much as twice their own body length to trap prey, and this move may increase the webs' area by a factor of up to ten. Experiments have shown that ''Deinopis spinosus'' has two different techniques for trapping prey: backwards strikes to catch flying insects, whose vibrations it detects; and forward strikes to catch ground-walking prey that it sees. These two techniques have also been observed in other deinopids. Walking insects form most of the prey of most deinopids, but one population of ''Deinopis subrufa'' appears to live mainly on Tipulidae, tipulid flies that they catch with the backwards strike. Mature female bolas spiders of the genus ''Mastophora (spider), Mastophora'' build "webs" that consist of only a single "trapeze line", which they patrol. They also construct a
bolas A bolas (plural: ''bolas'' or ''bolases''; from Spanish ''bola'', "ball", also known as ''boleadoras'') is a type of throwing weapon A weapon, arm or armament is any implement or device that can be used with the intent to inflict damage or ...

bolas
made of a single thread, tipped with a large ball of very wet sticky silk. They emit chemicals that resemble the pheromones of moths, and then swing the bolas at the moths. Although they miss on about 50% of strikes, they catch about the same weight of insects per night as web-weaving spiders of similar size. The spiders eat the bolas if they have not made a kill in about 30 minutes, rest for a while, and then make new bolas. Juveniles and adult males are much smaller and do not make bolas. Instead they release different pheromones that attract Drain fly, moth flies, and catch them with their front pairs of legs. The primitive
Liphistiidae The spider family Liphistiidae, recognized by Tamerlan Thorell in 1869, comprises 8 genera and about 100 species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as w ...
, the "trapdoor spiders" of the family Ctenizidae and many
tarantula Tarantulas comprise a group of large and often hairy spiders of the family Theraphosidae. Currently, 1,010 species have been identified. The term "tarantula" is usually used to describe members of the family Theraphosidae, although many oth ...

tarantula
s are ambush predators that lurk in burrows, often closed by trapdoors and often surrounded by networks of silk threads that alert these spiders to the presence of prey. Other ambush predators do without such aids, including many crab spiders, and a few species that prey on bees, which see ultraviolet, can adjust their ultraviolet reflectance to match the flowers in which they are lurking. Wolf spiders, jumping spiders, fishing spiders and some crab spiders capture prey by chasing it, and rely mainly on vision to locate prey. Some jumping spiders of the
genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification In biology, taxonomy () is the scientific study of naming, defining (Circumscription (taxonomy), circumscribing) and classifying gr ...
''
Portia Thomson Financial was an arm of the Thomson Corporation, an information provider. When the Thomson Corporation merged with Reuters to form Thomson Reuters in April 2008, Thomson Financial was merged with the business of Reuters to form the Markets ...
'' hunt other spiders in ways that seem intelligent, outflanking their victims or luring them from their webs. Laboratory studies show that ''Portia''s instinctive tactics are only starting points for a trial-and-error approach from which these spiders learn very quickly how to overcome new prey species. However, they seem to be relatively slow "thinkers", which is not surprising, as their brains are vastly smaller than those of mammalian predators. Ant mimicry, Ant-mimicking spiders face several challenges: they generally develop slimmer abdomens and false "waists" in the
cephalothorax The cephalothorax, also called prosoma in some groups, is a tagma of various arthropod An arthropod (, (gen. ποδός)) is an invertebrate Invertebrates are animals that neither possess nor develop a vertebral column (commonly known as a ...
to mimic the three distinct regions (tagmata) of an ant's body; they wave the first pair of legs in front of their heads to mimic antenna (biology), antennae, which spiders lack, and to conceal the fact that they have eight legs rather than six; they develop large color patches round one pair of eyes to disguise the fact that they generally have eight simple eyes, while ants have two compound eyes; they cover their bodies with reflective bristles to resemble the shiny bodies of ants. In some spider species, males and females mimic different ant species, as female spiders are usually much larger than males. Ant-mimicking spiders also modify their behavior to resemble that of the target species of ant; for example, many adopt a zig-zag pattern of movement, ant-mimicking jumping spiders avoid jumping, and spiders of the genus ''Synemosyna'' walk on the outer edges of leaves in the same way as ''Pseudomyrmex''. Ant mimicry in many spiders and other arthropods may be for protection from predators that hunt by sight, including birds, lizards and spiders. However, several ant-mimicking spiders prey either on ants or on the ants' "livestock", such as aphids. When at rest, the ant-mimicking crab spider ''Amyciaea'' does not closely resemble ''Oecophylla'', but while hunting it imitates the behavior of a dying ant to attract worker ants. After a kill, some ant-mimicking spiders hold their victims between themselves and large groups of ants to avoid being attacked.


Defense

There is strong evidence that spiders' coloration is camouflage that helps them to evade their major predators, birds and parasitic wasps, both of which have good color vision. Many spider species are colored so as to merge with their most common backgrounds, and some have disruptive coloration, stripes and blotches that break up their outlines. In a few species, such as the Hawaiian happy-face spider, ''Theridion grallator'', several coloration schemes are present in a ratio that appears to remain constant, and this may make it more difficult for predators to recognize the species. Most spiders are insufficiently dangerous or unpleasant-tasting for Aposematism, warning coloration to offer much benefit. However, a few species with powerful venom, large jaws or irritant bristles have patches of warning colors, and some actively display these colors when threatened. Many of the family Theraphosidae, which includes
tarantula Tarantulas comprise a group of large and often hairy spiders of the family Theraphosidae. Currently, 1,010 species have been identified. The term "tarantula" is usually used to describe members of the family Theraphosidae, although many oth ...

tarantula
s and Harpactirinae, baboon spiders, have urticating hairs on their abdomens and use their legs to flick them at attackers. These bristles are fine setae (bristles) with fragile bases and a row of barbs on the tip. The barbs cause intense irritation but there is no evidence that they carry any kind of venom. A few defend themselves against wasps by including networks of very robust threads in their webs, giving the spider time to flee while the wasps are struggling with the obstacles. The golden wheeling spider, ''Wheel spider, Carparachne aureoflava'', of the Namibian desert escapes parasitic wasps by flipping onto its side and Cartwheel (gymnastics), cartwheeling down sand dunes.


Socialization

A few spider species that build webs live together in large colonies and show social behavior, although not as complex as in Eusociality, social insects. ''Anelosimus Anelosimus eximius, eximius'' (in the family (biology), family Theridiidae) can form colonies of up to 50,000 individuals. The genus ''Anelosimus'' has a strong tendency towards sociality: all known American species are social, and species in Madagascar are at least somewhat social. Members of other species in the same family but several different genera have convergent evolution, independently developed social behavior. For example, although ''Theridion nigroannulatum'' belongs to a
genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification In biology, taxonomy () is the scientific study of naming, defining (Circumscription (taxonomy), circumscribing) and classifying gr ...
with no other social species, ''T. nigroannulatum'' build colonies that may contain several thousand individuals that co-operate in prey capture and share food. Other communal spiders include several ''Philoponella'' species (family
Uloboridae Uloboridae is a family In human society A society is a Social group, group of individuals involved in persistent Social relation, social interaction, or a large social group sharing the same spatial or social territory, typically subje ...
), ''Agelena consociata'' (family Agelenidae) and ''Mallos (spider), Mallos Mallos gregalis, gregalis'' (family Dictynidae). Social predatory spiders need to defend their prey against kleptoparasites ("thieves"), and larger colonies are more successful in this. The herbivorous spider '''' lives in small colonies which help to protect eggs and spiderlings. Even widow spiders (genus ''Latrodectus''), which are notoriously cannibalistic, have formed small colonies in captivity, sharing webs and feeding together. In experiments, spider species like ''Steatoda grossa'', ''Latrodectus hesperus'' and ''Hobo spider, Eratigena agrestis'' stayed away from ''Myrmica rubra'' ant colonies. These ants are predators and Pheromone#Trail, pheromones they release for communication have a notable deterrent effect on these spider species.


Web types

There is no consistent relationship between the classification of spiders and the types of web they build: species in the same
genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification In biology, taxonomy () is the scientific study of naming, defining (Circumscription (taxonomy), circumscribing) and classifying gr ...
may build very similar or significantly different webs. Nor is there much correspondence between spiders' classification and the chemical composition of their silks. Convergent evolution in web construction, in other words use of similar techniques by remotely related species, is rampant. Orb web designs and the spinning behaviors that produce them are the best understood. The basic radial-then-spiral sequence visible in orb webs and the sense of direction required to build them may have been inherited from the common ancestors of most spider groups. However, the majority of spiders build non-orb webs. It used to be thought that the sticky orb web was an evolutionary innovation resulting in the diversification of the Orbiculariae. Now, however, it appears that non-orb spiders are a subgroup that evolved from orb-web spiders, and non-orb spiders have over 40% more species and are four times as abundant as orb-web spiders. Their greater success may be because sphecid wasps, which are often the dominant predators of spiders, much prefer to attack spiders that have flat webs.


Orb

About half the potential prey that hit orb webs escape. A web has to perform three functions: intercepting the prey (intersection), absorbing its momentum without breaking (stopping), and trapping the prey by entangling it or sticking to it (retention). No single design is best for all prey. For example: wider spacing of lines will increase the web's area and hence its ability to intercept prey, but reduce its stopping power and retention; closer spacing, larger sticky droplets and thicker lines would improve retention, but would make it easier for potential prey to see and avoid the web, at least during the day. However, there are no consistent differences between orb webs built for use during the day and those built for use at night. In fact, there is no simple relationship between orb web design features and the prey they capture, as each orb-weaving species takes a wide range of prey. The hubs of orb webs, where the spiders lurk, are usually above the center, as the spiders can move downwards faster than upwards. If there is an obvious direction in which the spider can retreat to avoid its own predators, the hub is usually offset towards that direction. Horizontal orb webs are fairly common, despite being less effective at intercepting and retaining prey and more vulnerable to damage by rain and falling debris. Various researchers have suggested that horizontal webs offer compensating advantages, such as reduced vulnerability to wind damage; reduced visibility to prey flying upwards, because of the backlighting from the sky; enabling oscillations to catch insects in slow horizontal flight. However, there is no single explanation for the common use of horizontal orb webs. Spiders often attach highly visible silk bands, called decorations or stabilimenta, to their webs. Field research suggests that webs with more decorative bands captured more prey per hour. However, a laboratory study showed that spiders reduce the building of these decorations if they sense the presence of predators. There are several unusual variants of orb web, many of them convergently evolved, including: attachment of lines to the surface of water, possibly to trap insects in or on the surface; webs with twigs through their centers, possibly to hide the spiders from predators; "ladderlike" webs that appear most effective in catching moths. However, the significance of many variations is unclear. The orb-weaving species, ''Zygiella x-notata,'' for example, is known for its characteristic missing sector orb web. The missing sector contains a signal thread used to detect prey vibrations on the female's web. In 1973, Skylab 3 took two orb-web spiders into space to test their web-spinning capabilities in zero gravity. At first, both produced rather sloppy webs, but they adapted quickly.


Cobweb

Members of the family Theridiidae weave irregular, tangled, three-dimensional webs, popularly known as cobwebs. There seems to be an evolutionary trend towards a reduction in the amount of sticky silk used, leading to its total absence in some species. The construction of cobwebs is less stereotyped than that of orb-webs, and may take several days.


Other

The Linyphiidae generally make horizontal but uneven sheets, with tangles of stopping threads above. Insects that hit the stopping threads fall onto the sheet or are shaken onto it by the spider, and are held by sticky threads on the sheet until the spider can attack from below.


Web design in zero gravity

Many experiments have been conducted to study the effect of zero gravity on the design of spider webs. In late 2020, reports of recent experiments were published that indicated that although web design was affected adversely in zero gravity conditions, having access to a light source could orient spiders and enable them to build their normally shaped webs under such conditions.


Evolution


Fossil record

Although the fossil record of spiders is considered poor, almost 1000 species have been described from fossils. Because spiders' bodies are quite soft, the vast majority of fossil spiders have been found preserved in amber. The oldest known amber that contains fossil arthropods dates from in the Early Cretaceous period. In addition to preserving spiders' anatomy in very fine detail, pieces of amber show spiders mating, killing prey, producing silk and possibly caring for their young. In a few cases, amber has preserved spiders' egg sacs and webs, occasionally with prey attached; the oldest fossil web found so far is 100 million years old. Earlier spider fossils come from a few lagerstätten, places where conditions were exceptionally suited to preserving fairly soft tissues. The oldest known exclusively terrestrial
arachnid Arachnida () is a class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytica ...

arachnid
is the trigonotarbid ''Palaeotarbus jerami'', from about in the Silurian period, and had a triangular
cephalothorax The cephalothorax, also called prosoma in some groups, is a tagma of various arthropod An arthropod (, (gen. ποδός)) is an invertebrate Invertebrates are animals that neither possess nor develop a vertebral column (commonly known as a ...
and segmented abdomen, as well as eight legs and a pair of
pedipalp Pedipalps (commonly shortened to palps or palpi) are the second pair of appendage An appendage (or outgrowth) is an external body part, or natural prolongation, that protrudes from an organism In biology, an organism () is any orga ...
s. ''Attercopus fimbriunguis'', from in the
Devonian The Devonian ( ) is a geologic period and system of the Paleozoic The Paleozoic (or Palaeozoic) Era ( ; from the Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the H ...
period, bears the earliest known silk-producing spigots, and was therefore hailed as a spider at the time of its discovery. However, these spigots may have been mounted on the underside of the abdomen rather than on
spinneret A spinneret is a silk Silk is a natural fiber, natural protein fiber, some forms of which can be weaving, woven into textiles. The protein fiber of silk is composed mainly of fibroin and is produced by certain insect larvae to form coc ...
s, which are modified
appendage An appendage (or outgrowth) is an external body part, or natural prolongation, that protrudes from an organism's body. In invertebrate biology, an appendage refers to any of the homology (biology), homologous body parts that may extend from a ...
s and whose mobility is important in the building of webs. Hence ''Attercopus'' and the similar Permian arachnid ''Permarachne'' may not have been true spiders, and probably used silk for lining nests or producing egg cases rather than for building webs. The largest known fossil spider as of 2011 is the araneid ''Nephila jurassica'', from about , recorded from Daohuogo, Inner Mongolia in China. Its body length is almost 25 mm, (i.e., almost one inch). Several
Carboniferous The Carboniferous ( ) is a geologic period The geologic time scale (GTS) is a system of chronological dating that classifies Geology, geological strata (stratigraphy) in time. It is used by geologists, paleontology, paleontologists, and other ...
spiders were members of the
Mesothelae The Mesothelae are a suborder of spider Spiders ( order Araneae) are air-breathing arthropod An arthropod (, (gen. ποδός)) is an invertebrate animal having an exoskeleton, a Segmentation (biology), segmented body, and paired jointed a ...
, a primitive group now represented only by the
Liphistiidae The spider family Liphistiidae, recognized by Tamerlan Thorell in 1869, comprises 8 genera and about 100 species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as w ...
. The mesothelid ''Paleothele montceauensis'', from the Late
Carboniferous The Carboniferous ( ) is a geologic period The geologic time scale (GTS) is a system of chronological dating that classifies Geology, geological strata (stratigraphy) in time. It is used by geologists, paleontology, paleontologists, and other ...
over , had five spinnerets. Although the Permian period saw rapid Adaptive radiation, diversification of flying
insect Insects (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Rom ...

insect
s, there are very few fossil spiders from this period. The main groups of modern spiders,
Mygalomorphae The Mygalomorphae, or mygalomorphs, are an infraorder In biological classification In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, che ...
and
Araneomorphae The Araneomorphae (also called the Labidognatha) are an infraorder In biological classification In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Bioch ...

Araneomorphae
, first appear in the Triassic well before . Some Triassic mygalomorphs appear to be members of the family Hexathelidae, whose modern members include the notorious Sydney funnel-web spider, and their spinnerets appear adapted for building funnel-shaped webs to catch jumping insects.
Araneomorphae The Araneomorphae (also called the Labidognatha) are an infraorder In biological classification In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Bioch ...

Araneomorphae
account for the great majority of modern spiders, including those that weave the familiar orb-shaped webs. The Jurassic and Cretaceous periods provide a large number of fossil spiders, including representatives of many modern families.


External relationships

The spiders (Araneae) are monophyletic (i.e., a clade, consisting of a last common ancestor and all of its descendants). There has been debate about what their closest evolutionary relatives are, and how all of these evolved from the ancestral chelicerates, which were marine animals. This 2019 cladogram illustrates the spiders' phylogenetic relationships. Arachnids lack some features of other chelicerates, including backward-pointing mouths and gnathobases ("jaw bases") at the bases of their legs; both of these features are part of the ancestral
arthropod An arthropod (, (gen. ποδός)) is an invertebrate Invertebrates are animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This includes all animals apart fr ...
feeding system. Instead, they have mouths that point forwards and downwards, and all have some means of breathing air. Spiders (Araneae) are distinguished from other arachnid groups by several characteristics, including
spinneret A spinneret is a silk Silk is a natural fiber, natural protein fiber, some forms of which can be weaving, woven into textiles. The protein fiber of silk is composed mainly of fibroin and is produced by certain insect larvae to form coc ...
s and, in males,
pedipalp Pedipalps (commonly shortened to palps or palpi) are the second pair of appendage An appendage (or outgrowth) is an external body part, or natural prolongation, that protrudes from an organism In biology, an organism () is any orga ...
s that are specially adapted for sperm transfer.


Internal relationships

The cladogram shows the relation among spider suborders and families:


Taxonomy

Spiders are divided into two suborders,
Mesothelae The Mesothelae are a suborder of spider Spiders ( order Araneae) are air-breathing arthropod An arthropod (, (gen. ποδός)) is an invertebrate animal having an exoskeleton, a Segmentation (biology), segmented body, and paired jointed a ...
and Opisthothelae, of which the latter contains two infraorders,
Mygalomorphae The Mygalomorphae, or mygalomorphs, are an infraorder In biological classification In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, che ...
and
Araneomorphae The Araneomorphae (also called the Labidognatha) are an infraorder In biological classification In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Bioch ...

Araneomorphae
. Over 48,000 living
species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individu ...

species
of spiders (order Araneae) have been identified and as of 2019 grouped into 120 family (biology), families and about 4,100 genus, genera by arachnology, arachnologists.


Mesothelae

The only living members of the primitive Mesothelae are the family
Liphistiidae The spider family Liphistiidae, recognized by Tamerlan Thorell in 1869, comprises 8 genera and about 100 species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as w ...
, found only in Southeast Asia, China, and Japan. Most of the Liphistiidae construct silk-lined burrows with thin trapdoors, although some species of the genus ''Liphistius'' build camouflaged silk tubes with a second trapdoor as an emergency exit. Members of the genus ''Liphistius'' run silk "tripwires" outwards from their tunnels to help them detect approaching prey, while those of the genus ''Heptathela'' do not and instead rely on their built-in vibration sensors. Spiders of the genus ''Heptathela'' have no venom glands, although they do have venom gland outlets on the fang tip. Full text at The extinct families Arthrolycosidae, found in
Carboniferous The Carboniferous ( ) is a geologic period The geologic time scale (GTS) is a system of chronological dating that classifies Geology, geological strata (stratigraphy) in time. It is used by geologists, paleontology, paleontologists, and other ...
and Permian rocks, and Arthromygalidae, so far found only in
Carboniferous The Carboniferous ( ) is a geologic period The geologic time scale (GTS) is a system of chronological dating that classifies Geology, geological strata (stratigraphy) in time. It is used by geologists, paleontology, paleontologists, and other ...
rocks, have been classified as members of the Mesothelae.


Mygalomorphae

The Mygalomorphae, which first appeared in the Triassic period, are generally heavily built and ″hairy″, with large, robust
chelicerae The chelicerae () are the mouthparts of the Chelicerata, an arthropod An arthropod (, (gen. ποδός)) is an invertebrate animal having an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form ...

chelicerae
and fangs (technically, spiders do not have true hairs, but rather setae). Well-known examples include
tarantula Tarantulas comprise a group of large and often hairy spiders of the family Theraphosidae. Currently, 1,010 species have been identified. The term "tarantula" is usually used to describe members of the family Theraphosidae, although many oth ...

tarantula
s, Ctenizidae, ctenizid trapdoor spiders and the Australasian funnel-web spiders. Most spend the majority of their time in burrows, and some run silk tripwires out from these, but a few build webs to capture prey. However, mygalomorphs cannot produce the pirifom silk that the Araneomorphae use as an instant adhesive to glue silk to surfaces or to other strands of silk, and this makes web construction more difficult for mygalomorphs. Since mygalomorphs rarely "Ballooning (spider), balloon" by using air currents for transport, their populations often form clumps. In addition to arthropods, some mygalomorphs are known to prey on frogs, small mammals, lizards, snakes, snails, and small birds.


Araneomorphae

In addition to accounting for over 90% of spider species, the Araneomorphae, also known as the "true spiders", include orb-web spiders, the cursorial s, and jumping spiders, as well as the only known herbivorous spider, ''''. They are distinguished by having fangs that oppose each other and cross in a pinching action, in contrast to the Mygalomorphae, which have fangs that are nearly parallel in alignment.


Human interaction


Bites

Although spiders are widely feared, only a few species are dangerous to people. Spiders will only bite humans in self-defense, and few produce worse effects than a mosquito bite or bee sting. Most of those with medically serious bites, such as recluse spiders (genus ''Loxosceles'') and widow spiders (genus ''Latrodectus''), would rather flee and bite only when trapped, although this can easily arise by accident. The defensive tactics of Australian funnel-web spiders (family Atracidae) include fang display. Their venom, although they rarely inject much, has resulted in 13 attributed human deaths over 50 years. They have been deemed to be the world's most dangerous spiders on clinical and venom toxicity grounds, though this claim has also been attributed to the Brazilian wandering spider (genus ''Phoneutria''). There were about 100 reliably reported deaths from spider bites in the 20th century, compared to about 1,500 from jellyfish stings. Many alleged cases of spider bites may represent incorrect diagnoses, which would make it more difficult to check the effectiveness of treatments for genuine bites. A review published in 2016 agreed with this conclusion, showing that 78% of 134 published medical case studies of supposed spider bites did not meet the necessary criteria for a spider bite to be verified. In the case of the two genera with the highest reported number of bites, ''Loxosceles'' and ''Latrodectus'', spider bites were not verified in over 90% of the reports. Even when verification had occurred, details of the treatment and its effects were often lacking. Because spider silk is both light and very strong, BioSteel, attempts are being made to produce it in goats' milk and in the leaves of plants, by means of genetic engineering.


Arachnophobia

Arachnophobia is a specific phobia—it is the abnormal fear of spiders or anything reminiscent of spiders, such as webs or spiderlike shapes. It is one of the most common specific phobias, and some statistics show that 50% of women and 10% of men show symptoms. It may be an exaggerated form of an instinctive response that helped early humans to survive, or a cultural phenomenon that is most common in predominantly European societies.


As food

Spiders are used as food. Cooked
tarantula Tarantulas comprise a group of large and often hairy spiders of the family Theraphosidae. Currently, 1,010 species have been identified. The term "tarantula" is usually used to describe members of the family Theraphosidae, although many oth ...

tarantula
s are considered a delicacy in Cambodia, and by the Piaroa Indians of southern Venezuela – provided the highly irritant bristles, the spiders' main defense system, are removed first.


Spiders in culture

Spiders have been the focus of stories and mythologies of various cultures for centuries. Uttu, the Sumerian religion, ancient Sumerian goddess of weaving, was envisioned as a spider spinning her web. According to her main myth, she resisted her father Enki's sexual advances by ensconcing herself in her web, but let him in after he promised her fresh produce as a marriage gift, thereby allowing him to Alcohol intoxication, intoxicate her with beer and rape her. Enki's wife Ninhursag heard Uttu's screams and rescued her, removing Enki's semen from her vagina and planting it in the ground to produce eight previously-nonexistent plants. In a story told by the Roman poet Ovid in his ''Metamorphoses'', Arachne was a Lydian girl who challenged the goddess Athena to a weaving contest. Arachne won, but Athena destroyed her tapestry out of jealousy, causing Arachne to hang herself. In an act of mercy, Athena brought Arachne back to life as the first spider. Stories about the trickster-spider Anansi are prominent in the oral tradition, folktales of West Africa and the Caribbean. In some cultures, spiders have symbolized patience due to their hunting technique of setting webs and waiting for prey, as well as mischief and malice due to their venomous bites. The Italian tarantella is a dance to rid the young woman of the lustful effects of a spider bite. Web-spinning also caused the association of the spider with creation myths, as they seem to have the ability to produce their own worlds. Dreamcatchers are depictions of spiderwebs. The Moche culture, Moche people of ancient Peru worshipped nature. They placed emphasis on animals and often depicted spiders in their art.Berrin, Katherine & Larco Museum. ''The Spirit of Ancient Peru: Treasures from the Larco Museum, Museo Arqueológico Rafael Larco Herrera.'' New York: Thames and Hudson, 1997.


See also

* Glossary of spider terms * List of endangered spiders * Spider taxonomy * Arachnidism * Toxins#Biotoxins, Toxins * List of animals that produce silk


Footnotes


Bibliography

* *


Further reading

* * * * * * *


External links

*
Picture story about the jumping spider ''Aelurillus v-insignitus''

New Mexico State University "The Spiders of the Arid Southwest"


* [https://web.archive.org/web/20110511234340/http://media.library.uiuc.edu/cgi/b/bib/bix-idx?type=simple&c=bix&sid=54d8a20e4f1eb5f2de074bad4caba7ae&Submit=search&sort=title&q1=spiders&rgn1=Entire+record list of field guides to spiders], from the International Field Guides database * * The Spider World Record: https://peerj.com/articles/3972/ {{good article Spiders, Articles containing video clips Carboniferous arachnids Extant Pennsylvanian first appearances Taxa named by Carl Alexander Clerck