Bolas spider
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A bolas spider is a member of the
orb-weaver spider Orb-weaver spiders are members of the spider family Araneidae. They are the most common group of builders of spiral wheel-shaped webs often found in gardens, fields, and forests. The English word "orb" can mean "circular", hence the English name ...
(family Araneidae) that, instead of spinning a typical orb web, hunts by using one or more sticky "capture blobs" on the end of a
silk Silk is a natural protein fiber, some forms of which can be woven into textiles. The protein fiber of silk is composed mainly of fibroin and is produced by certain insect larvae to form cocoons. The best-known silk is obtained from the coc ...
line, known as a "
bolas Bolas or bolases (singular bola; from Spanish and Portuguese ''bola'', "ball", also known as a ''boleadora'' or ''boleadeira'') is a type of throwing weapon made of weights on the ends of interconnected cords, used to capture animals by entan ...
". By swinging the bolas at flying male
moth Moths are a paraphyletic group of insects that includes all members of the order Lepidoptera that are not butterflies, with moths making up the vast majority of the order. There are thought to be approximately 160,000 species of moth, many of w ...
s or moth flies nearby, the spider may snag its prey rather like a fisherman snagging a fish on a hook. Because of this, they are also called angling or fishing spiders (although the remotely related genus ''
Dolomedes ''Dolomedes'' is a genus of large spiders of the family Pisauridae. They are also known as fishing spiders, raft spiders, dock spiders or wharf spiders. Almost all ''Dolomedes'' species are semiaquatic, with the exception of the tree-dwelling ...
'' is also called a fishing spider). The prey is lured to the spider by the production of up to three
sex pheromone Sex pheromones are pheromones released by an organism to attract an individual of the same species, encourage them to mate with them, or perform some other function closely related with sexual reproduction. Sex pheromones specifically focus on ind ...
-analogues. Bolas spiders have been treated as either the whole or part of either the tribe "Mastophoreae" or Mastophorini, the subfamily Mastophorinae, or the informal group mastophorines. Recent studies show that the genus ''
Celaenia ''Celaenia'' is a genus of South Pacific orb-weaver spiders first described by Tamerlan Thorell Tord Tamerlan Teodor Thorell (3 May 1830 – 22 December 1901) was a Swedish arachnologist. Thorell studied spiders with Giacomo Doria at the ...
'', which does not use a bolas, belongs in the same taxonomic group.


Description

Bolas spiders are small nocturnal animals with conspicuous outgrowths on the upper (dorsal) surface of the
cephalothorax The cephalothorax, also called prosoma in some groups, is a tagma of various arthropods, comprising the head and the thorax fused together, as distinct from the abdomen behind. (The terms ''prosoma'' and ''opisthosoma'' are equivalent to ''cepha ...
. Mature females have a body length of , while the males, which are very much smaller, have a body length usually less than . The abdomen of adult females is large relative to the cephalothorax, partially covering it. In some species, the female's abdomen is comparatively smooth, while in others it has humps and tubercules. The females of some bolas spiders (e.g. '' Mastophora cornigera'') look remarkably like a bird dropping, thanks to their large, globular abdomen and brownish cephalothorax. This is a form of defensive mimicry as the animals that prey on spiders pay little attention to bird droppings, which enables the spiders to rest unnoticed during the day in fairly exposed places. '' M. bisaccata'' resembles the shell of a snail that is abundant in the spider's habitat. While the bird dropping mimics rest on the upper surface of leaves, ''M. bisaccata'' rests on the undersides. If removed from the surface, '' Mastophora'' females produce a pungent odor, which is highly unusual for spiders (other than bolas spiders, only one species of ''
Cyrtarachne ''Cyrtarachne'' is a genus of Araneidae, orb-weaver spiders first described by Tamerlan Thorell in 1868. Species it contains fifty-five species: *''Cyrtarachne akirai, C. akirai'' Tanikawa, 2013 – China, Korea, Taiwan, Japan *''Cyrtarachne av ...
'' is known to do this). They do not attempt to flee when handled. Some species of ''
Cladomelea ''Cladomelea'' is a genus of African orb-weaver spiders first described by Eugène Simon in 1895. Adult females of the genus are bolas spider A bolas spider is a member of the orb-weaver spider (family Araneidae) that, instead of spinning a ...
'' also rest exposed on leaves during the day. However, the Australian ''
Ordgarius magnificus ''Ordgarius magnificus'', the magnificent spider, is a bolas spider in the family Araneidae. It is endemic to forests along the Australian east coast. Description Females are up to 14 mm long and almost as wide; males reach only 2 mm. ...
'', which displays eye spots on its back that make it resemble the moth it hunts, ties leaves together with silk to form a retreat.


Taxonomy


Genera

Bolas-using spiders are species of four related genera. (Distributions are from the
World Spider Catalog The World Spider Catalog (WSC) is an online searchable database concerned with spider taxonomy. It aims to list all accepted families, genera and species, as well as provide access to the related taxonomic literature. The WSC began as a series of ...
.) * ''
Cladomelea ''Cladomelea'' is a genus of African orb-weaver spiders first described by Eugène Simon in 1895. Adult females of the genus are bolas spider A bolas spider is a member of the orb-weaver spider (family Araneidae) that, instead of spinning a ...
'' Simon, 1895 – Central and South Africa * ''
Exechocentrus ''Exechocentrus'' is a genus of Madagascan orb-weaver spiders (family Araneidae) first described by Eugène Simon in 1889. It is a bolas-using spider, capturing its prey with one or more sticky drops at the end of a single line of silk rather ...
'' Simon, 1889
Madagascar Madagascar (; mg, Madagasikara, ), officially the Republic of Madagascar ( mg, Repoblikan'i Madagasikara, links=no, ; french: République de Madagascar), is an island country in the Indian Ocean, approximately off the coast of East Africa ...
* '' Mastophora'' Holmberg, 1876 (syn. ''Agathostichus'') – North and South America * ''
Ordgarius ''Ordgarius'' is a genus of orb-weaver spiders first described by Eugen von Keyserling in 1886. Adult females of the genus are bolas spiders, capturing their prey with one or more sticky drops at the end of a single line of silk rather than in ...
'' Keyserling, 1886 (syn. ''Dicrostichus'') – Australia north to India, China and Japan The use of a bolas by the Madagascan genus ''Exechocentrus'' was not reported until 2012, so the genus is not included in earlier accounts of bolas spiders.


Classification

Bolas spiders are members of the family Araneidae, the
orb-weaver spider Orb-weaver spiders are members of the spider family Araneidae. They are the most common group of builders of spiral wheel-shaped webs often found in gardens, fields, and forests. The English word "orb" can mean "circular", hence the English name ...
s, although they do not weave webs. They may be treated as a group within the subfamily
Cyrtarachninae Cyrtarachninae is a subfamily of spiders in the family Araneidae (orb-weaver spiders, araneids). The group has been circumscribed in several different ways. It originated as the group Cyrtarachneae, described by Eugène Simon in 1892. The group w ...
''sensu lato'', or as the whole or part of a separate taxon. In 1931, Mello-Leitão created a tribe under the name Mastophoreae, which included genera now known to use a bolas as well the genus ''
Acantharachne ''Acantharachne'' is a genus of African orb-weaver spiders first described by Albert Tullgren in 1910. Taxonomy The genus ''Acantharachne'' was erected by Albert Tullgren in 1910 for the species '' Acantharachne cornuta''. There was already a g ...
''. Gertsch in 1955 also placed bolas spiders in the tribe Mastophoreae, again including ''Acantharachne'' (under the synonym ''Acantharanea''). Article 29.2 of the
International Code of Zoological Nomenclature The International Code of Zoological Nomenclature (ICZN) is a widely accepted convention in zoology that rules the formal scientific naming of organisms treated as animals. It is also informally known as the ICZN Code, for its publisher, the ...
states that the ending "-ini" should be used for tribes, so the correct name for the tribe is now "Mastophorini". The tribe has been elevated to a separate subfamily Mastophorinae. The informal name "mastophorines" has also been used, including both bolas-using spiders and a related genus. A 2014
molecular phylogenetic Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...
study of a representative set of genera placed in Cyrtarachninae ''s.l.'' showed that the species of the two bolas spider genera included in the study formed a strongly supported clade nested within Cyrtarachninae ''s.l.'' A wider study of the family Araneidae published in 2020 reached a similar conclusion, separating Cyrtarachninae ''s.l.'' into two informal sister groups "mastophorines" and "cyrtarachines". Mastophorines included the genus ''
Celaenia ''Celaenia'' is a genus of South Pacific orb-weaver spiders first described by Tamerlan Thorell Tord Tamerlan Teodor Thorell (3 May 1830 – 22 December 1901) was a Swedish arachnologist. Thorell studied spiders with Giacomo Doria at the ...
'' that does not use a bolas. Bolas-using spiders thus form a subgroup within the narrowly defined mastophorines or the broadly defined Cyrtarachninae.


Phylogeny and web evolution

The Cyrtarachninae, defined broadly, construct several kinds of web, which differ from the orb webs of other Araneidae. Some construct " spanning-thread webs", which have a small number of radii and widely spaced sticky threads that do not form spirals. Others construct triangular webs. These are formed in the same way as spanning-thread webs, but with only three radii, so that they appear triangular. Bolas spiders do not spin webs at all, adult females catching their prey on single sticky threads. Finally, some species capture their prey without a web, using their outstretched legs, as do juvenile and male bolas spiders. One hypothesis was that the evolution of the web types involved successive reduction: spanning-thread webs → triangular webs → bolas → no web. However, the 2014 molecular phylogenetic study by Tanikawa ''et al.'' showed that this hypothesis did not fit with the evolutionary relationships they derived. Their cladogram is shown below. (The dashed line shows where the genus ''Exechocentrus'' would be expected to fall based on a 2020 study.) Triangular webs could have been derived from spanning-thread webs, but spiders with no webs or that used bolas formed a completely separate monophyletic group. Scharff ''et al.'' in a molecular phylogenetic study of the family Araneidae published in 2020 reached a similar conclusion concerning the relationships within the broadly defined Cyrtarachninae. They included the bolas-using genus ''
Exechocentrus ''Exechocentrus'' is a genus of Madagascan orb-weaver spiders (family Araneidae) first described by Eugène Simon in 1889. It is a bolas-using spider, capturing its prey with one or more sticky drops at the end of a single line of silk rather ...
'' in their analysis (which has been added to the cladogram above), dividing Cyrtarachninae ''s.l.'' into "mastophorines" and "cyrtarachnines".


Distribution

Bolas spiders are found in America, Africa including Madagascar, and Australasia northwards into Asia. They do not occur in temperate
Eurasia Eurasia (, ) is the largest continental area on Earth, comprising all of Europe and Asia. Primarily in the Northern and Eastern Hemispheres, it spans from the British Isles and the Iberian Peninsula in the west to the Japanese archipelago a ...
. About half of the known ''Mastophora'' species occur in
South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the southe ...
. The genus is distributed from southern
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to the northern US (to 45° north latitude in
Minnesota Minnesota () is a state in the upper midwestern region of the United States. It is the 12th largest U.S. state in area and the 22nd most populous, with over 5.75 million residents. Minnesota is home to western prairies, now given over to ...
). ''M. archeri'', ''M. bisaccata'', ''M. hutchinsoni'' and ''M. phrynosoma'' occur widely in the US east of the
Great Plains The Great Plains (french: Grandes Plaines), sometimes simply "the Plains", is a broad expanse of flatland in North America. It is located west of the Mississippi River and east of the Rocky Mountains, much of it covered in prairie, steppe, an ...
. ''M. cornigera'' occurs from
Alabama (We dare defend our rights) , anthem = "Alabama (state song), Alabama" , image_map = Alabama in United States.svg , seat = Montgomery, Alabama, Montgomery , LargestCity = Huntsville, Alabama, Huntsville , LargestCounty = Baldwin County, Al ...
to
California California is a U.S. state, state in the Western United States, located along the West Coast of the United States, Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the List of states and territori ...
, as well as in northern
Mexico Mexico (Spanish: México), officially the United Mexican States, is a country in the southern portion of North America. It is bordered to the north by the United States; to the south and west by the Pacific Ocean; to the southeast by Guatema ...
.


Life-cycle

The life-cycle of the North American '' Mastophora hutchinsoni'' is best known. As is probably the case for other ''Mastophora'' species in temperate regions, mating takes place in late summer or early fall, after which egg cases are produced. Adults do not survive the winter, males typically dying before females. A similar pattern is observed for bolas spiders in the Southern Hemisphere, depending on the climate. In the subtropical climate of
Edmonton Edmonton ( ) is the capital city of the Canadian province of Alberta. Edmonton is situated on the North Saskatchewan River and is the centre of the Edmonton Metropolitan Region, which is surrounded by Alberta's central region. The city ancho ...
in north Queensland, Australia, a female ''
Ordgarius monstrosus ''Ordgarius monstrosus'' is a species of spider in the orb-weaver spider family Araneidae, found in Queensland, Australia. ''O. monstrosus'' is a bolas spider. Rather than using a web, adult females catch their prey by using a line with one ...
'' matured in June and produced egg cases between late June and early September. In
Pietermaritzburg Pietermaritzburg (; Zulu: umGungundlovu) is the capital and second-largest city in the province of KwaZulu-Natal, South Africa. It was founded in 1838 and is currently governed by the Msunduzi Local Municipality. Its Zulu name umGungundlovu ...
, South Africa, adult females of ''
Cladomelea akermani ''Cladomelea akermani'' is a species of spider in the orb-weaver spider family Araneidae, found in South Africa. ''Cladomelea'' species, including ''C. akermani'', are "bolas spiders" – adult females capture their prey by using a sticky d ...
'' were observed with egg cases during July. The number of egg cases varies widely among species, with temperate species producing fewer than tropical ones (e.g. one to three for ''Mastophora'' species in temperate regions of the United States, and up to 11 for '' M. dizzydeani'' near the equator). The number of eggs per case also varies depending on the climate, so that the total number of spiderlings produced by one female ranges from several hundred in the temperate US to several thousand in
Colombia Colombia (, ; ), officially the Republic of Colombia, is a country in South America with insular regions in North America—near Nicaragua's Caribbean coast—as well as in the Pacific Ocean. The Colombian mainland is bordered by the Car ...
. Some male bolas spiders, such as those of '' Mastophora cornigera'' and ''
Ordgarius magnificus ''Ordgarius magnificus'', the magnificent spider, is a bolas spider in the family Araneidae. It is endemic to forests along the Australian east coast. Description Females are up to 14 mm long and almost as wide; males reach only 2 mm. ...
'', appear to be mature on emergence from their egg cases and so capable of inseminating females. Others, such as those of ''M. dizzydeani'', ''M. hutchinsoni'' and '' M. phrynosoma'' require one or two moults before becoming mature. By contrast, ''Mastophora'' females may require up to eight moults to reach maturity.


Prey capture

Bolas spiders are defined by the way in which adults catch their prey. Like other members of the subfamily Cyrtarachninae ''sensu lato'', bolas spiders specialize in catching
moth Moths are a paraphyletic group of insects that includes all members of the order Lepidoptera that are not butterflies, with moths making up the vast majority of the order. There are thought to be approximately 160,000 species of moth, many of w ...
s. The scales covering moth wings are detachable, so that most ordinary orb webs are not effective at capturing moths. Adult female bolas spiders spend the day resting, disguised in various ways, including as bird droppings. At night, they feed on male moths which they attract by producing a scent that mimics the
sex pheromone Sex pheromones are pheromones released by an organism to attract an individual of the same species, encourage them to mate with them, or perform some other function closely related with sexual reproduction. Sex pheromones specifically focus on ind ...
s emitted by the female of one or more species of moth. They capture approaching male moths by using a "
bolas Bolas or bolases (singular bola; from Spanish and Portuguese ''bola'', "ball", also known as a ''boleadora'' or ''boleadeira'') is a type of throwing weapon made of weights on the ends of interconnected cords, used to capture animals by entan ...
", a silken thread with one or more sticky drops at the end which they swing, rather than throw, at the moth. Other spiders in the subfamily Cyrtarachninae, including ''
Celaenia ''Celaenia'' is a genus of South Pacific orb-weaver spiders first described by Tamerlan Thorell Tord Tamerlan Teodor Thorell (3 May 1830 – 22 December 1901) was a Swedish arachnologist. Thorell studied spiders with Giacomo Doria at the ...
'' species from Australia and '' Taczanowskia'' species from South America, also use chemical lures to attract moths, but they catch them with their front legs. Bolas spiders will try and often succeed in catching any insect that is flying nearby. They seem able to detect prey by the sound of their approaching flight. In experiments, ''M. cornigera'' attacked a hand-held moth whose wings were fluttering, but did not attack if the moth's wings were immobilized. The manner in which the bolas is used differs among the genera. ''Mastophora'' species hold the bolas stationary with a front leg until a moth approaches, and then cock the leg and swing the bolas towards the prey with a rapid pendulum-like stroke. Other genera use their second leg. ''Ordgarius'' species begin to whirl the bolas rapidly when detecting an incoming moth. ''Cladomelea akermani'' whirls the bolas immediately after it has been prepared for about 15 minutes, even when there is no moth present. Instead of preparing a single bolas, at least four ''Mastophora'' species are known to sometimes hang up to nine droplets on one horizontal line. This has not been observed to result in prey capture, but is remarkably similar to the midline of a ''Pasilobus'' web in which the spanning threads have been broken. Spiderlings of both sexes and adult males hunt without a bolas. This might be because the small globule these spiders could produce would dry out rapidly. Rather, they position themselves at edges of leaves and grab prey with their frontal pair of legs. Juvenile females and males of all ages of ''M. hutchinsoni'' have a row of strong bristles on the prolateral surface of the
tibiae The tibia (; ), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outside of the tibia); it connects ...
and metatarsi of each of their first two pairs of legs which may aid in prey capture. Females lose these bristles after a few moults. Moth flies of the genus '' Psychoda'' are prominent prey of juvenile and adult male ''Mastophora''.


Drop structure

The sticky drops of the bolas have a diameter of about . Their internal structure is complex, consisting of a mass of curled or folded fibre embedded in a viscid matrix which is in turn surrounded by a less viscous layer. This results in the low viscosity liquid flowing past the moth's scales to reach the cuticle below, while the more viscous liquid forms a bond to the thread to sustain the moth's weight. The folded thread inside the ball permits elastic elongations which extend the spider's striking range. ''Ordgarius'' sometimes has smaller droplets above the terminal one. ''
Exechocentrus lancearius ''Exechocentrus lancearius'' is a species of spider in the orb-weaver spider family Araneidae, found only in Madagascar. It was initially described from a partial specimen of an adult female. The first description of a complete specimen and its ...
'' uses a bolas with two globules. The other genera usually produce only one terminal globule. The drop shrinks over time, thus presumably reducing its effectiveness in catching prey. Bolas spiders consume unused bolas after at most half an hour if the hunt was fruitless.


Prey variety

Female ''Mastophora'' catch an average of two moths per night, but as many as six or seven catches during a single night have been observed. Bolas spiders vary in the range of moth species they capture, with 20 moth species recorded for '' Mastophora cornigera'' females, mostly noctuids, and four for '' Mastophora hutchinsoni'' females, three of which were noctuids. A study of ''M. hutchinsoni'' showed that the blend of chemicals produced by the spider was very similar to that produced by the female of the bristly cutworm, '' Lacinipolia renigera'', whose males make up about two thirds of the biomass consumed by the spider. A study by K.F. Haynes showed that ''M. hutchinsoni'' females adapt to changes in prey availability, with one major prey species flying from early evening until 10:30 pm or so and the other only after 11:00 pm. The first moth ignores the pheromone of the second, so the spider produces a mix of both pheromones early in the evening. However, since the second moth is repulsed by the other moth's pheromone, the spider ceases to produce the first pheromone later at night.


Natural enemies

Yeargan noted that records of natural enemies of bolas spiders all concern predators or parasitoids of the egg stage. A gryllacridid was observed feeding on the eggs of ''
Ordgarius magnificus ''Ordgarius magnificus'', the magnificent spider, is a bolas spider in the family Araneidae. It is endemic to forests along the Australian east coast. Description Females are up to 14 mm long and almost as wide; males reach only 2 mm. ...
'', and a
flesh fly Sarcophagidae () are a family (biology), family of fly, flies commonly known as flesh flies. They differ from most flies in that they are Ovoviviparity, ovoviviparous, opportunistically depositing hatched or hatching maggots instead of eggs on c ...
parasitoid In evolutionary ecology, a parasitoid is an organism that lives in close association with its host (biology), host at the host's expense, eventually resulting in the death of the host. Parasitoidism is one of six major evolutionarily stable str ...
has been reared from egg cases of the same species. Five species of
hymenoptera Hymenoptera is a large order (biology), order of insects, comprising the sawfly, sawflies, wasps, bees, and ants. Over 150,000 living species of Hymenoptera have been described, in addition to over 2,000 extinct ones. Many of the species are Par ...
n parasitoids are known to attack ''Mastophora'' eggs. '' Tromatobia notator'' parasitizes ''M. cornigera'', ''M. bisaccata'' and ''M. phrynosoma''; a '' Gelis'' species parasitizes ''M. cornigera''. Eupelmids in the genus '' Arachnophaga'' also parasitize ''Mastophora'' species.


References


Bibliography

* *


External links


Description, Australian distribution and pictures of ''Ordgarius magnificus''





Science Spider Friday: Bolas spiders
{{DEFAULTSORT:Bolas Spiders Araneidae Arthropod common names