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Pseudoscorpions, also known as false scorpions or book scorpions, are small, scorpion-like
arachnid Arachnida () is a class of joint-legged invertebrate animals (arthropods), in the subphylum Chelicerata. Arachnida includes, among others, spiders, scorpions, ticks, mites, pseudoscorpions, harvestmen, camel spiders, whip spiders and vinegaro ...
s belonging to the order Pseudoscorpiones, also known as Pseudoscorpionida or Chelonethida. Pseudoscorpions are generally beneficial to humans since they prey on
clothes moth Clothes moth or clothing moth is the common name for several species of moth considered to be pests, whose larvae eat animal fibres (hairs), including clothing and other fabrics. These include: * ''Tineola bisselliella'', the common clothes mot ...
larvae, carpet beetle larvae,
booklice Psocoptera are a paraphyletic group of insects that are commonly known as booklice, barklice or barkflies. The name Psocoptera has been replaced with Psocodea in recent literature, with the inclusion of the former order Phthiraptera into Psocode ...
,
ant Ants are eusocial insects of the family Formicidae and, along with the related wasps and bees, belong to the order Hymenoptera. Ants evolved from vespoid wasp ancestors in the Cretaceous period. More than 13,800 of an estimated total of 22,0 ...
s, mites, and small
flies Flies are insects of the order Diptera, the name being derived from the Greek δι- ''di-'' "two", and πτερόν ''pteron'' "wing". Insects of this order use only a single pair of wings to fly, the hindwings having evolved into advanced ...
. They are tiny, and are rarely noticed due to their small size, despite being common in many environments. When people do see pseudoscorpions, especially indoors, they are often mistaken for
tick Ticks (order Ixodida) are parasitic arachnids that are part of the mite superorder Parasitiformes. Adult ticks are approximately 3 to 5 mm in length depending on age, sex, species, and "fullness". Ticks are external parasites, living by ...
s or small spiders. Pseudoscorpions often carry out
phoresis Phoresis or phoresy is a non-permanent, commensalistic interaction in which one organism (a phoront or phoretic) attaches itself to another (the host) solely for the purpose of travel. Phoresis has been observed directly in ticks and mites s ...
, a form of
commensalism Commensalism is a long-term biological interaction (symbiosis) in which members of one species gain benefits while those of the other species neither benefit nor are harmed. This is in contrast with mutualism, in which both organisms benefit fr ...
in which one organism uses another for the purpose of transport.


Characteristics

Pseudoscorpions belong to the class
Arachnida Arachnida () is a class of joint-legged invertebrate animals (arthropods), in the subphylum Chelicerata. Arachnida includes, among others, spiders, scorpions, ticks, mites, pseudoscorpions, harvestmen, camel spiders, whip spiders and vinegaro ...
. They are small arachnids with a flat, pear-shaped body, and pincer-like pedipalps that resemble those of scorpions. They usually range from in length. Pennsylvania State University, Department
Entomological Notes: Pseudoscorpion Fact Sheet
/ref> The largest known species is ''
Garypus titanius ''Garypus titanius'', the giant pseudoscorpion, is the largest species of pseudoscorpion—small, scorpion-looking creatures—in the world. Critically endangered, it is restricted to Boatswain Bird Island, a small rocky island off Ascension Isl ...
'' of
Ascension Island Ascension Island is an isolated volcanic island, 7°56′ south of the Equator in the South Atlantic Ocean. It is about from the coast of Africa and from the coast of South America. It is governed as part of the British Overseas Territory of ...
at up to . Range is generally smaller at an average of . A pseudoscorpion has eight legs with five to seven segments each; the number of fused segments is used to distinguish families and genera. They have two very long pedipalps with palpal chelae (pincers), which strongly resemble the pincers found on a scorpion. The pedipalps generally consist of an immobile "hand" and mobile "finger", the latter controlled by an adductor muscle. Members of the clade Iocheirata, which contains the majority of pseudoscorpions, are venomous, with a venom gland and duct usually located in the mobile finger; the venom is used to immobilize the pseudoscorpion's prey. During digestion, pseudoscorpions exude a mildly corrosive fluid over the prey, then ingest the liquefied remains. The abdomen, referred to as the opisthosoma, is made up of twelve segments, each protected by sclerotized plates (called tergites above and sternites below). The abdomen is short and rounded at the rear, rather than extending into a segmented tail and stinger like true scorpions. The color of the body can be yellowish-tan to dark-brown, with the paired claws often a contrasting color. They may have two, four or no eyes. Pseudoscorpions spin silk from a gland in their jaws to make disk-shaped
cocoon Cocoon may refer to: *Cocoon (silk), a pupal casing made by moth caterpillars and other insect larvae *Apache Cocoon, web development software * ''Cocoon'' (film), a 1985 science fiction-fantasy film **'' Cocoon: The Return'', 1988 sequel to ''Coco ...
s for mating, molting, or waiting out cold weather, but they do not have
book lungs A book lung is a type of respiration organ used for atmospheric gas exchange that is present in many arachnids, such as scorpions and spiders. Each of these organs is located inside an open ventral abdominal, air-filled cavity (atrium) and conn ...
like true scorpions and the
Tetrapulmonata Tetrapulmonata is a non-ranked supra-ordinal clade of arachnids. It is composed of the extant orders Thelyphonida (whip scorpions), Schizomida (short-tailed whip scorpions), Amblypygi (tail-less whip scorpions) and Araneae (spiders). It is the ...
. Instead, they breathe exclusively through tracheae, which open laterally through two pairs of spiracles on the posterior margins of the sternites of abdominal segments 3 and 4.


Behavior

Some species have an elaborate
mating dance A courtship display is a set of display behaviors in which an animal, usually a male, attempts to attract a mate; the mate exercises choice, so sexual selection acts on the display. These behaviors often include ritualized movement ("dances"), ...
, where the male pulls a female over a spermatophore previously laid upon a surface. In other species, the male also pushes the sperm into the female genitals using the forelegs. The female carries the fertilized eggs in a brood pouch attached to her
abdomen The abdomen (colloquially called the belly, tummy, midriff, tucky 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 torso. ...
, and the young ride on the mother for a short time after they hatch. Between 20 and 40 young are hatched in a single brood, with more than one brood per year possible. The young go through three molts over the course of several years before reaching adulthood. Many species molt in a small, silken igloo that protects them from enemies during this vulnerable period. After reaching adulthood, pseudoscorpions live 2–3 years. They are active in the warm months of the year, overwintering in silken cocoons when the weather grows cold. Smaller species live in debris and
humus In classical soil science, humus is the dark organic matter in soil that is formed by the decomposition of plant and animal matter. It is a kind of soil organic matter. It is rich in nutrients and retains moisture in the soil. Humus is the Latin ...
. Some species are
arboreal Arboreal locomotion is the locomotion of animals in trees. In habitats in which trees are present, animals have evolved to move in them. Some animals may scale trees only occasionally, but others are exclusively arboreal. The habitats pose nu ...
, while others are phagophiles, eating parasites in an example of
cleaning symbiosis Cleaning symbiosis is a mutually beneficial association between individuals of two species, where one (the cleaner) removes and eats parasites and other materials from the surface of the other (the client). Cleaning symbiosis is well-known amon ...
. Some species are
phoretic Phoresis or phoresy is a non-permanent, commensalistic interaction in which one organism (a phoront or phoretic) attaches itself to another (the host) solely for the purpose of travel. Phoresis has been observed directly in ticks and mites s ...
, others may sometimes be found feeding on mites under the wing covers of certain beetles.


Distribution

More than 3,300 species of pseudoscorpions are recorded in more than 430 genera, with more being discovered on a regular basis. They range worldwide, even in temperate to cold regions such as
Northern Ontario Northern Ontario is a primary geographic and quasi-administrative region of the Canadian province of Ontario, the other primary region being Southern Ontario. Most of the core geographic region is located on part of the Superior Geological Provi ...
and above the timberline in Wyoming's Rocky Mountains in the United States and the
Jenolan Caves The Jenolan Caves (Tharawal: ''Binoomea'', ''Bindo'', ''Binda'') are limestone caves located within the Jenolan Karst Conservation Reserve in the Central Tablelands region, west of the Blue Mountains, in Jenolan, Oberon Council, New South Wal ...
of Australia, but have their most dense and diverse populations in the tropics and subtropics, where they spread even to island territories such as the Canary Islands, where around 25 endemic species have been found. There are also two endemic species on the
Maltese Islands Malta ( , , ), officially the Republic of Malta ( mt, Repubblika ta' Malta ), is an island country in the Mediterranean Sea. It consists of an archipelago, between Italy and Libya, and is often considered a part of Southern Europe. It lies ...
. Species have been found under tree bark, in leaf and pine litter, in soil, in tree hollows, under stones, in caves such as the
Movile Cave Movile Cave () is a cave near Mangalia, Constanța County, Romania discovered in 1986 by Cristian Lascu a few kilometers from the Black Sea coast. It is notable for its unique groundwater ecosystem abundant in hydrogen sulfide and carbon diox ...
, at the seashore in the intertidal zone, and within fractured rocks. '' Chelifer cancroides'' is the species most commonly found in homes, where it is often observed in rooms with dusty books. There, the tiny animals () can find their food such as booklice and
house dust mites House dust mites (HDM, or simply dust mites) are various species of acariform mites belonging to the family Pyroglyphidae that are found in association with dust in dwellings. They are known for causing allergies. Biology Species The current ...
. They enter homes by riding insects ( phoresy) larger than themselves, or are brought in with firewood.


Evolution

The oldest known fossil pseudoscorpion, '' Dracochela deprehendor'' is known from
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- homologous, differing in their origin, structu ...
fragments of nymphs found in the
Panther Mountain Formation The Panther Mountain Formation is a geologic formation in New York. It preserves fossils dating back to the Devonian period. It is located in the counties of Albany, Madison, Oneida, Otsego, and Schoharie. It is well known for its fossil art ...
near Gilboa in
New York New York most commonly refers to: * New York City, the most populous city in the United States, located in the state of New York * New York (state), a state in the northeastern United States New York may also refer to: Film and television * ...
, dating to the mid- Devonian, around 383 million years ago. It has all of the traits of a modern pseudoscorpion, indicating that the order evolved very early in the history of land animals. Its morphology suggests that it is more primitive than any living pseudoscorpion. As with most other arachnid orders, the pseudoscorpions have changed very little since they first appeared, retaining almost all the features of their original form. After the Devonian fossils, almost no other fossils of pseudoscorpions are known for over 250 million years until Cretaceous fossils in
amber Amber is fossilized tree resin that has been appreciated for its color and natural beauty since Neolithic times. Much valued from antiquity to the present as a gemstone, amber is made into a variety of decorative objects."Amber" (2004). In Ma ...
, all belonging to modern families, suggesting that the major diversification of pseudoscorpions had already taken place by this time. The only fossil from this time gap is '' Archaeofeaella'' from the
Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...
of Ukraine, approximately 227 million years ago, which is suggested to be an early relative of the family Feaellidae.


Historical references

Pseudoscorpions were first described by Aristotle, who probably found them among scrolls in a library where they would have been feeding on
booklice Psocoptera are a paraphyletic group of insects that are commonly known as booklice, barklice or barkflies. The name Psocoptera has been replaced with Psocodea in recent literature, with the inclusion of the former order Phthiraptera into Psocode ...
. Robert Hooke referred to a "Land-Crab" in his 1665 work '' Micrographia''. Another reference in the 1780s, when George Adams wrote of "a lobster-insect, spied by some labouring men who were drinking their porter, and borne away by an ingenious gentleman, who brought it to my lodging."


Classification

The following taxon numbers are calculated as of the end of 2012. * Order Pseudoscorpiones De Geer, 1778 (2 suborders) :::* † Family Dracochelidae Schawaller, Shear and Bonamo, 1991 (1 fossil genus, 1 fossil species) ::* Superfamily
Chthonioidea The Chthonioidea are a superfamily of pseudoscorpion Pseudoscorpions, also known as false scorpions or book scorpions, are small, scorpion-like arachnids belonging to the order Pseudoscorpiones, also known as Pseudoscorpionida or Chelonethida. ...
Daday, 1888 (2 families) :::* Family Chthoniidae Daday, 1888 (44 genera, 700+ species fossil species :::* Family Pseudotyrannochthoniidae Beier, 1932 (5 genera, 49 species) ::* Superfamily
Feaelloidea The Feaelloidea are a superfamily of pseudoscorpion Pseudoscorpions, also known as false scorpions or book scorpions, are small, scorpion-like arachnids belonging to the order Pseudoscorpiones, also known as Pseudoscorpionida or Chelonethida. ...
Ellingsen, 1906 (2 families) :::* Family Feaellidae Ellingsen, 1906 (1 genus, 12 species) :::* Family
Pseudogarypidae The Pseudogarypidae are a small family of pseudoscorpions. Most recent species are found in North America, while one species is endemic to Tasmania. Species * '' Neopseudogarypus'' J.C.H. Morris, 1948 :* '' Neopseudogarypus scutellatus'' J.C.H. ...
Chamberlin, 1923 (2 genera, 7 species fossil species :* Suborder Iocheirata Harvey, 1992 (5 superfamilies) ::* Superfamily Neobisioidea Chamberlin, 1930 (7 families) :::* Family Bochicidae Chamberlin, 1930 (12 genera, 42 species) :::* Family Gymnobisiidae Beier, 1947 (4 genera, 11 species) :::* Family Hyidae Chamberlin, 1930 (2 genera, 14 species) :::* Family Ideoroncidae Chamberlin, 1930 (11 genera, 59 species) :::* Family
Neobisiidae Neobisiidae is a family of pseudoscorpions distributed throughout Africa, the Americas and Eurasia and consist of 550 species in 32 genera. Some species live in caves while some are surface-dwelling. Characteristics The body color ranges from re ...
Chamberlin, 1930 (33 genera, 595 species fossil species :::* Family Parahyidae Harvey, 1992 (1 genus, 1 species) :::* Family Syarinidae Chamberlin, 1930 (18 genera, 111 species) ::* Superfamily
Garypoidea The Garypoidea are a superfamily of pseudoscorpion Pseudoscorpions, also known as false scorpions or book scorpions, are small, scorpion-like arachnids belonging to the order Pseudoscorpiones, also known as Pseudoscorpionida or Chelonethida. ...
Simon, 1879 (6 families) :::* Family Garypidae Simon, 1879 (10 genera, 80 species) :::* Family Garypinidae Daday, 1888 (21 genera, 76 species fossil species :::* Family Geogarypidae Chamberlin, 1930 (3 genera, 60 species fossil species :::* Family Larcidae Harvey, 1992 (2 genera, 15 species) :::* Family Menthidae Chamberlin, 1930 (5 genera, 12 species) :::* Family Olpiidae Banks, 1895 (36 genera, 268 species) ::* Superfamily Cheiridioidea Hansen, 1894 (2 families) :::* Family Cheiridiidae Hansen, 1894 (7 genera, 73 species fossil genus, 3 fossil species :::* Family Pseudochiridiidae Chamberlin, 1923 (2 genera, 12 species fossil species ::* Superfamily
Sternophoroidea The Sternophoridae are a family of pseudoscorpions with about 20 described species in three genera. While ''Afrosternophorus'' is an Old World genus, found mainly in Australasia (with, despite its name, only one African species), the other two ge ...
Chamberlin, 1923 (1 family) :::* Family Sternophoridae Chamberlin, 1923 (3 genera, 20 species) ::* Superfamily
Cheliferoidea The Cheliferoidea are a superfamily of pseudoscorpion Pseudoscorpions, also known as false scorpions or book scorpions, are small, scorpion-like arachnids belonging to the order Pseudoscorpiones, also known as Pseudoscorpionida or Chelonethida. ...
Risso, 1827 (4 families) :::* Family Atemnidae Kishida, 1929 (21 genera, 178 species fossil genus, 1 fossil species :::* Family Cheliferidae Risso, 1827 (58 genera, 273 species fossil genus, 12 fossil species :::* Family Chernetidae Menge, 1855 (117 genera, 663 species fossil genus, 3 fossil species :::* Family Withiidae Chamberlin, 1931 (36 genera, 158 species fossil genus, 1 fossil species


Cladogram

After Benavides et al, 2019, with historic taxonomic groups from Harvey (1992).


References


Further reading

* Mark Harvey (2011)
Pseudoscorpions of the World
* Joseph C. Chamberlin (1931): ''The Arachnid Order Chelonethida''. Stanford University Publications in Biological Science. 7(1): 1–284. * Clarence Clayton Hoff (1958): List of the Pseudoscorpions of North America North of Mexico. ''American Museum Novitates''. 1875
PDF
* Max Beier (1967): Pseudoscorpione vom kontinentalen Südost-Asien. ''Pacific Insects'' 9(2): 341–369
PDF
* * P. D. Gabbutt (1970): Validity of Life History Analyses of Pseudoscorpions. ''Journal of Natural History'' 4: 1–15. * W. B. Muchmore (1982): ''Pseudoscorpionida''. In "Synopsis and Classification of Living Organisms." Vol. 2. Parker, S.P. * J. A. Coddington, S. F. Larcher & J. C. Cokendolpher (1990): ''The Systematic Status of Arachnida, Exclusive of Acari, in North America North of Mexico.'' In "Systematics of the North American Insects and Arachnids: Status and Needs." National Biological Survey 3. ''Virginia Agricultural Experiment Station, Virginia Polytechnic Institute and State University''. * Mark S. Harvey (1991): ''Catalogue of the Pseudoscorpionida.'' (edited by V . Mahnert). Manchester University Press, Manchester.


External links

* *
Video of Pseudoscorpions in Ireland
{{Authority control Extant Devonian first appearances