Solifugae
Temporal range: [1]
Solifuge from Arizona
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Chelicerata
Class: Arachnida
Order: Solifugae
Sundevall, 1833

Solifugae is an order of animals in the class Arachnida known variously as camel spiders, wind scorpions, sun spiders, or solifuges. The order includes more than 1,000 described species in about 147 genera. Despite the common names, they are neither true scorpions (order Scorpiones), nor true spiders (order Araneae). Most species of Solifugae live in dry climates and feed opportunistically on ground-dwelling arthropods and other small animals. The largest species grow to a length of 12–15 cm (5–6 in), including legs. A number of urban legends exaggerate the size and speed of the Solifugae, and their potential danger to humans, which is negligible.

Anatomy

Ventral aspect of a solifuge, showing respiratory slots

Solifuges are moderately small to large arachnids (a few millimeters to several centimeters in body length), with the larger species reaching 12–15 cm (5–6 in) in length, including legs.[2][3] In practice, the respective lengths of the legs of various species differ greatly, so the resulting figures are often misleading. More practical measurements refer primarily to the body length, quoting leg lengths separately, if at all. The body length is up to 7 cm (3 in).[4][5] Most species are closer to 5 cm (2 in) long, and some small species are under 1 cm (0.4 in) in head-plus-body length when mature.[6]

Like that of the spider order, the Araneae, the body plan of the Solifugae has two main tagmata: the prosoma, or cephalothorax, is the anterior tagma, and the 10-segmented abdomen, or opisthosoma, is the posterior tagma. The abdominal tergites and sternites are separated by large areas of intersegmental membranes, giving it a high degree of flexibility and ability to stretch considerably, which allows it to consume a large amount of food.[7] As shown in the illustrations, the solifuge prosoma and opisthosoma are not separated by nearly as clear a constriction and connecting tube or "pedicel" as occurs in Araneae. The lack of the pedicel reflects another difference between the Solifugae and spiders, namely that solifuges lack both spinnerets and silk, and do not spin webs. Spiders need considerable mobility of their abdomens in their spinning activities, and the Solifugae have no such adaptation.

The prosoma comprises the head, the mouthparts, and the somites that bear the legs and the pedipalps. It is covered by a carapace, also called a prosomal dorsal shield or peltidium, which is composed of three distinct elements called propeltidium, mesopeltidium and metapeltidium. The propeltidium contains the eyes, the chelicerae that, in most species, are conspicuously large, the pedipalps and the first two pairs of legs. Meso- and metapeltidium contains the third and fourth pairs of legs.[8][6][9] The chelicerae serve as jaws and in many species also are used for stridulation. Unlike scorpions, solifuges do not have a third tagma that forms a "tail".

Currently, neither fossil nor embryological evidence shows that arachnids ever had a separate thorax-like division, so the validity of the term cephalothorax, which means a fused cephalon, or head, and thorax, has been questioned. Also, arguments exist against use of "abdomen", as the opisthosoma of many arachnids contains organs atypical of an abdomen, such as a heart and respiratory organs.[10]

Like other arachnids outside the orders of scorpions and the Tetrapulmonata, the Solifugae lack book lungs, having instead a well-developed tracheal system that inhales and exhales air through a number of spiracles - one pair between the second and third pair of walking legs, two pairs on the abdomen on abdominal segments three and four, and an unpaired spiracle on the fifth abdominal segment.[11] As embryos they also have opisthosomal protuberances resembling the pulmonary sacs found in some palpigrades.[12]

Chelicerae

Chewing movement of the chelicerae in solifuges dorsal view (top) and side view (bottom)
Lateral aspect of chelicera, showing teeth and cutting edge

Among the most distinctive features of the Solifugae are their large chelicerae, which in many species are longer than the prosoma. Each of the two chelicerae has two articles (segments, parts connected by a joint),[13] forming a powerful pincer, much like that of a crab; each article bears a variable number of teeth, largely depending on the species.[6][9] The chelicerae of many species are surprisingly strong; they are capable of shearing hair or feathers from vertebrate prey or carrion, and of cutting through skin and thin bones such as those of small birds.[14] Many Solifugae stridulate with their chelicerae, producing a rattling noise.[3]

Legs and pedipalps

Male solifuge in South African veld: Its flagella are visible near the tips of the chelicerae, looking like large, backward-curling bristles. As in most species, it holds its pedipalps clear of the ground; its front legs serve as tactile sensors, barely touching the ground with their setae.

These elements work the same way as in most other arachnids. Although the Solifugae appear to have five pairs of legs, only the hind four pairs are true legs. Each true leg has seven segments: coxa, trochanter, femur, patella, tibia, metatarsus, and tarsus.[14][15]

The first, or anterior, of the five pairs of leg-like appendages are not "actual" legs, but pedipalps, and they have only five segments each. The pedipalps of the Solifugae function partly as sense organs similar to insects' antennae, and partly in locomotion, feeding, and fighting. In normal locomotion, they do not quite touch the ground, but are held out to detect obstacles and prey; in that attitude, they look particularly like an extra pair of legs or perhaps arms. Reflecting the great dependence of the Solifugae on their tactile senses, their anterior true legs commonly are smaller and thinner than the posterior three pairs. That smaller anterior pair acts largely in a sensory role as a supplement to the pedipalps, and in many species they accordingly lack tarsi. At the tips of their pedipalps, Solifugae bear a membranous suctorial organ, which are used for capturing prey, and also for bringing water to their mouthparts for drinking and climbing smooth surfaces.[16][14][17]

A female of a species in the family Solpugidae showing the malleoli beneath the posterior pair of legs

For the most part, only the posterior three pairs of legs are used for running.[9][14] On the undersides of the coxae and trochanters of the last pair of legs, the Solifugae have fan-shaped sensory organs called malleoli or racquet (or racket) organs. Sometimes, the blades of the malleoli are directed forward, sometimes not. They have been suspected to be sensory organs for the detection of vibrations in the soil, perhaps to detect threats and potential prey or mates.[14] These structures may be chemoreceptors.[18]: 66 

Males are usually smaller than females, with relatively longer legs.[3] Unlike females, the males bear a pair of flagella, one on each chelicera. In the accompanying photograph of a male solifuge, one flagellum is just visible near the tip of each chelicera. The flagella, which bend back over the chelicerae, are sometimes called horns and are believed to have some sexual connection, but their function has not yet been clearly explained.[14]

Eyes

Solifuge eyes with bristles

Some species have very large central eyes. They look like simple eyes or ocelli, but are quite sophisticated. They can recognise forms, and are used in hunting and avoiding enemies. These eyes may represent the last step in the integration of the aggregate of simple ocelli into a compound eye, and of further integration of a compound eye into a simple eye.[19] Lateral vestigial eyes can be found inserted into pits on the inner side of the cuticle. The lenses of these eyes are usually atrophied, but in some species there are both nerves and pigment cells present, and their function could be to detect motions or changes in light intensity.[20]

Classification and Phylogeny

The Solifugae are an order of their own, though are sometimes confused with spiders, which form a completely distinct order, the Araneae. The order comprises over 1200 described species in 146 genera assigned to these 16 families:[21][22]

Suborder Australosolifugae

Suborder Boreosolifugae

incertae sedis

In 2023, the internal phylogeny of solifuges was resolved for the first time using phylogenomics.[23] The molecular phylogeny of the order showed evidence for two groups of families, which were recognized as suborders. Boreosolifugae comprises five families predominantly from the Northern Hemisphere (Eremobatidae, Gylippidae, Karschiidae, Galeodidae, and Rhagodidae). Australosolifugae comprises seven families predominantly from the Southern Hemisphere (Ammotrechidae, Ceromidae, Daesiidae, Hexisopodidae, Melanoblossidae, Mummuciidae, and Solpugidae). Daesiidae and Ammotrechidae were both recovered as non-monophyletic, due to the nested position of Melanoblossidae inside Daesiidae, and the nested position of Mummuciidae inside Ammotrechidae. A subsequent genomic study established three additional families: Dinorhaxidae (formerly within Melanoblossidae) was recovered as part of Boreosolifugae; and Lipophagidae (formerly within Gylippidae) and Namibesiidae (formerly within Daesiidae) were recovered as part of Australosolifugae.[22] This phylogeny is considered congruent with a Gondwanan origin for Australosolifugae and a Laurasian origin for Boreosolifugae.[23]

Ecology

Gluvia dorsalis eating a cabbage bug (Eurydema oleracea)

Although the Solifugae are considered to be endemic indicators of desert biomes,[6]: 1  they occur widely in semidesert and scrub. Some species also live in grassland or forest habitats. The Solifugae generally inhabit warm and arid habitats, including virtually all warm deserts and scrublands in all continents except Antarctica and Australia.[3]

Solifugae species are carnivorous or omnivorous, with most feeding on termites, darkling beetles, and other small, ground-dwelling arthropods. They are aggressive hunters and voracious opportunistic feeders, and have been recorded as feeding on snakes, small lizards, birds, and rodents.[6] Prey is located with the pedipalps and killed and cut into pieces by the chelicerae. The prey is then liquefied, and the liquid ingested through the pharynx. Although they do not normally attack humans, their chelicerae can penetrate human skin, and painful bites have been reported.[3]

Various other predators, such as the large slit-faced bat, scorpions, toads, and insectivores, may prey on the Solifugae.

Life cycle

The Solifugae are typically univoltine (reproducing once a year).[6]: 8  Reproduction can involve direct or indirect sperm transfer; when indirect, the male emits a spermatophore on the ground and then inserts it with his chelicerae in the female's genital pore. To do this, he flings the female on her back.

The female then digs a burrow, into which she lays 50 to 200 eggs; some species then guard them until they hatch. Because the female does not feed during this time, she tries to fatten herself beforehand, and a species of 5 cm (2.0 in) has been observed to eat more than 100 flies during that time in the laboratory.[3] The Solifugae undergo a number of stages including, egg, postembryo, 9–10 nymphal instars, and adults.[6]

Etymology

The name Solifugae derives from Latin, and means "those that flee from the sun". The order is also known by the names Solpugida, Solpugides, Solpugae, Galeodea, and Mycetophorae. Their common names include camel spider, wind scorpion, scorpion carrier, jerrymunglum,[24] sun scorpion, and sun spider. In southern Africa, they are known by a host of names, including red romans, haarskeerders ("hair cutters"), and baardskeerders ("beard cutters"), the latter two relating to the belief they use their formidable jaws to clip hair from humans and animals to line their subterranean nests.[25]

Solifuges and humans

A scorpion (left) fighting a solifuge (right)

Solifuges have been recognized as distinct taxa from ancient times. In Aelian's De natura animalium, "four-jawed spiders" are credited, along with scorpions, as being responsible for the abandoning of a desert region near the Astaboras river (said to be in India, but thought to be a river in Ethiopia).[26] Anton August Heinrich Lichtenstein theorized in 1797 that the "mice" that plagued the Philistines in the Old Testament were Solifugae. During World War I, troops stationed in Abū Qīr, Egypt, would stage fights between captive "jerrymanders", as they referred to them, and placed bets on the outcome. Similarly, British troops stationed in Libya in World War II staged fights between solifuges and scorpions.[6]: 2–3 

Urban legends

The Solifugae are the subject of many legends and exaggerations about their size, speed, behavior, appetite, and lethality. They are not especially large, the biggest having a leg span around 12 cm (4.7 in).[3] They are fast on land compared to other invertebrates, with their top speed estimated to be 16 km/h (10 mph),[2] close to half as fast as the fastest human sprinter.[27]

The Solifugae apparently have neither venom glands nor any venom-delivery apparatus such as the fangs of spiders, stings of wasps, or venomous setae of caterpillars (e.g., Lonomia or Acharia species).[28] One 1978 study is frequently quoted, in which the authors report detection of an exception in India, in that Rhagodes nigrocinctus had venom glands, and that injection of the secretion into mice was frequently fatal. However, no supporting studies have confirmed either statement, such as by independent detection of the glands as claimed, or the relevance of the observations, if correct. Even the authors of the original account admitted to having found no means of delivery of the putative venom by the animal, and the only means of administering the material to the mice was by parenteral injection.[29] Given that many non-venoms such as saliva, blood and glandular secretions can be lethal if injected, and that no venomous function was even speculated upon in this study, there is still no evidence for even one venomous species of solifuge.[28]

Because of their unfamiliar spider-like appearance and rapid movements, Solifugae have startled or even frightened many people. This fear was sufficient to drive a family from their home when one was allegedly discovered in a soldier's house in Colchester, England, and caused the family to blame the solifuge for the death of their pet dog.[30] An Arizona resident developed painful lesions due to a claimed solifuge bite but could not produce a specimen for confirmation.[31] Though they are not venomous, the powerful chelicerae of a large specimen may inflict a painful nip, but nothing medically significant.[32]

Claims that Solifugae aggressively chase people are also untrue, as they are merely trying to stay in the shade/shadow provided by the human.[33]

References

  1. ↑ "Solifugae (camel spider)". Paleobiology Database.
  2. 1 2 "Egyptian giant solpugid (camel spider) Galeodes arabs". National Geographic. 11 April 2010. Archived from the original on January 21, 2010. Retrieved June 10, 2011.
  3. 1 2 3 4 5 6 7 Schimdt, G. (1993). Giftige und gefährliche Spinnentiere (in German). Westarp Wissenschaften. ISBN 3-89432-405-8.
  4. ↑ Pechenik, Jan (1996). Biology of the Invertebrates. Dubuque: Wm. C. Brown Publishers. ISBN 0-697-13712-0.
  5. ↑ Mullen, Gary R. (2009). Medical and Veterinary Entomology (2 ed.). Burlington, Massachusetts: Academic Press. ISBN 978-0-12-372500-4.
  6. 1 2 3 4 5 6 7 8 Fred Punzo (1998). The Biology of Camel-Spiders. Springer. ISBN 0-7923-8155-6. Retrieved January 25, 2010.
  7. ↑ The Biology Of Camel-spiders: Arachnida, Solifugae
  8. ↑ Dunlop, Jason A.; Krüger, Jessica; Alberti, Gerd (31 July 2012). "The sejugal furrow in camel spiders and acariform mites". Arachnologische Mitteilungen. 43: 29–36. doi:10.5431/aramit4303.
  9. 1 2 3 Barnes, Robert D. (1982). Invertebrate Zoology. Philadelphia, PA: Holt-Saunders International. pp. 613–614. ISBN 0-03-056747-5.
  10. ↑ Shultz, Stanley; Shultz, Marguerite (2009). The Tarantula Keeper's Guide. Hauppauge, New York: Barron's. p. 23. ISBN 978-0-7641-3885-0.
  11. ↑ Ax, Peter (2000). "Solifugae". Multicellular Animals: The Phylogenetic System of the Metazoa. Translated by Kinsey, S. Berlin: Springer. pp. 125–126. ISBN 9783662103968.
  12. ↑ Ballesteros, Jesús A.; Santibáñez López, Carlos E.; Kováč, Ľubomír; Gavish-Regev, Efrat; Sharma, Prashant P. (18 December 2019). "Ordered phylogenomic subsampling enables diagnosis of systematic errors in the placement of the enigmatic arachnid order Palpigradi". Proceedings of the Royal Society B: Biological Sciences. 286 (1917): 20192426. doi:10.1098/rspb.2019.2426. PMC 6939912. PMID 31847768.
  13. ↑ Brown, Lesley (1993). The New shorter Oxford English dictionary on historical principles. Oxford: Clarendon Press. ISBN 0-19-861271-0.
  14. 1 2 3 4 5 6 Holm, Erik; Dippenaar-Schoeman, Ansie (2010). Goggo Guide: The arthropods of southern Africa. Pretoria: LAPA Publishers. ISBN 978-0799346893.
  15. ↑ Filmer, Martin (1997). Southern African Spiders. City: BHB International / Struik. ISBN 1-86825-188-8.
  16. ↑ A sticky situation: Solifugids (Arachnida, Solifugae) use adhesive organs on their pedipalps for prey capture
  17. ↑ Harmer, Sir Sidney Frederic; Shipley, Arthur Everett et alia: The Cambridge natural history Volume 4, Crustacea, Trilobites, Arachnida, Tardigrada, Pentastomida etc. Macmillan Company 1895
  18. ↑ Punzo, Fred (1998). The Biology of Camel-Spiders: Arachnida, Solifugae. Boston, MA: Springer US. ISBN 9781461557272.
  19. ↑ Beklemishev, Vladimir (1969). Principles of Comparative Anatomy of Invertebrates. Chicago: University of Chicago Press. ISBN 0226041751.
  20. ↑ The Biology of Camel-Spiders: Arachnida, Solifugae
  21. ↑ "World Solifugae Catalog". World Solifugae Catalog. Natural History Museum Bern. Retrieved 5 June 2022.
  22. 1 2 Kulkarni, Siddharth S.; Yamasaki, Takeshi; Thi Hong Phung, Luong; Karuaera, Nanguei; Daniels, Savel R.; Gavish-Regev, Efrat; Sharma, Prashant P. (2024-02-01). "Phylogenomic data reveal three new families of poorly studied Solifugae (camel spiders)". Molecular Phylogenetics and Evolution. 191: 107989. doi:10.1016/j.ympev.2023.107989. ISSN 1055-7903. PMID 38072141. S2CID 266166984.
  23. 1 2 Kulkarni, Siddharth S.; Steiner, Hugh G.; Garcia, Erika L.; Iuri, Hernán; Jones, R. Ryan; Ballesteros, Jesús A.; Gainett, Guilherme; Graham, Matthew R.; Harms, Danilo; Lyle, Robin; Ojanguren-Affilastro, Andrés A.; Santibañez-López, Carlos E.; Silva de Miranda, Gustavo; Cushing, Paula E.; Gavish-Regev, Efrat (September 2023). "Neglected no longer: Phylogenomic resolution of higher-level relationships in Solifugae". iScience. 26 (9): 107684. Bibcode:2023iSci...26j7684K. doi:10.1016/j.isci.2023.107684. ISSN 2589-0042. PMC 10484990. PMID 37694155.
  24. ↑ Skaife, Sydney Harold; South African Nature Notes, Second edition. Pub: Maskew Miller: Cape Town, 1954.
  25. ↑ Ross Piper (2007). Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals. Greenwood Press.
  26. ↑ "Aelian, NA. 17.40". attalus.org. Retrieved March 6, 2019. - where they are called "four-jawed spiders".
  27. ↑ "IAAF (International Association of Athletics Federations) Biomechanical Research Project: Berlin 2009" (PDF). Archived from the original (PDF) on 2014-05-14. Retrieved 2013-11-18.
  28. 1 2 Klann, Anja Elisabeth (2009). Histology and Ultrastructure of Solifuges: Comparative Studies of Organ Systems of Solifuges (Arachnida, Solifugae) with Special Focus on Functional Analyses and Phylogenetic Interpretations (Dr. rer. nat. thesis). Universität Greifswald.
  29. ↑ Aruchami, M.; Sundara Rajulu, G. (1978). "An investigation on the poison glands and the nature of the venom of Rhagodes nigrocinctus (Solifugae: Arachnida)". Natl. Acad. Sci. Lett. 1: 191–192.
  30. ↑ Siddique, Haroon (2008-08-28). "Paratrooper's family flees home after Afghan spider 'kills dog'". The Guardian. Retrieved 2019-08-01.
  31. ↑ Sung, Jenny (July 27, 2017). "Mystery bug bite leaves Arizona man covered in bruises, 'excruciating pain'". Global News. Archived from the original on 2022-08-04. Retrieved July 27, 2017.
  32. ↑ David Penney (2009). "Solifugae (camel spiders)". Common Spiders and Other Arachnids of The Gambia, West Africa. Siri Scientific Press. p. 71. ISBN 978-0-9558636-3-9.
  33. ↑ Szalay, Jessie (17 December 2014). "Camel Spiders: Facts & Myths". livescience.com. Purch Group. Live Science. Retrieved 19 July 2023.

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