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Solifugae

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Solifugae
Temporal range: Late Carboniferous–Recent
Male solifugid, family Solpugidae, in veld near Uniondale, Western Cape.
Scientific classification
Kingdom:
Animalia
Phylum:
Arthropoda
Class:
Arachnida
Subclass:
Dromopoda
Order:
Solifugae

Sundevall, 1833
Families

see text

Solifugae is an order of animals in the class Arachnida. They are known variously as camel spiders, wind scorpions, sun spiders or solifuges. The order includes more than 1,000 described species in about 153 genera. The Solifugae is a different order from the true spiders (order Araneae) and the scorpions (order Scorpiones). Much like a spider, the body of a Solifugid has two tagmata: an opisthosoma (abdomen) behind the prosoma (that is, in effect, a combined head and thorax). At the front end, the prosoma bears two chelicerae that, in most species, are conspicuously large. The chelicerae serve as jaws and in many species also are used for stridulation. Unlike scorpions, solifugids do not have a third tagma that forms a "tail". Most species of Solifugae live in deserts and feed opportunistically on ground-dwelling arthropods and other small animals. Some species may grow to a length of 300 mm (12 in) including legs. A number of urban legends exaggerate the size and speed of Solifugae, and their potential danger to humans, which is practically nil.

Anatomy

Ventral aspect of a Solifugid, showing respiratory slots

Solifugae are moderately small to large arachnids (a few millimeters to several centimeters in body length), with the larger species reaching 15 cm (6 in) in head-and-body length.[1] Figures quoting implausible sizes for sensational effect are seldom useful because when they are not outright fictitious they usually include leg lengths in non-standard ways. In practice, the respective lengths of the legs of various species differ drastically, so the resulting figures are often misleading. More practical measurements refer primarily to the body length, quoting leg lengths separately, if at all. Even so, it remains difficult to get solidly supported data because very few sources quote anything better than anecdotal claims. One source suggests a body length of up to 7 cm (3 in)[2] Another gives a figure of 10 cm (4 in).[3] Even if one takes values such as 15 cm at face value, they are extremes. Most species are closer to 5 cm long, and some small species are under 1 cm in head-plus-body length when mature.[4]

The body has two main parts (tagmata). The prosoma, or cephalothorax, is the anterior tagma, and the ten-segmented abdomen, or opisthosoma, is the posterior part. As shown in the illustrations, the Solifugid prosoma and opisthosoma are not separated by nearly as clear a constriction as occurs in "true" spiders, the order Araneae. The prosoma comprises the head, the mouthparts and the somites that bear the legs and the pedipalps. The alternative name "cephalothorax" reflects the fact that the prosoma includes the parts that in insects form the head plus the thorax. Though it is not split into two clear tagmata, the prosoma does have a large, relatively well-defined anterior carapace, bearing the animal's eyes and chelicerae, while a smaller posterior section bears the legs.[4][5] Like pseudoscorpions and harvestmen, Solifugae lack book lungs, having instead a well-developed tracheal system that takes in air through three pairs of slits on the animal's underside.

Chelicerae

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,[6]) forming a powerful pincer, much like that of a crab's; each article bears a variable number of teeth, largely depending on the species.[4][5] 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.[7] Many Solifugae stridulate with their chelicerae, producing a rattling noise.[8]

Legs and pedipalps

Although Solifugae appear to have ten legs, they actually only have eight, as most other arachnids do. Each true leg has seven segments: coxa, trochanter, femur, patella, tibia, metatarsus, tarsus.[9][7] The first of the five pairs of appendages are not "true" legs, but pedipalps; they only have five segments each. The pedipalps of 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. Reflecting the great dependence of Solifugae on their tactile senses, their anterior true legs are commonly smaller and thinner than the posterior three pairs. That smaller anterior pair act 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 eversible adhesive organs, which they may use to capture flying prey, and which at least some species certainly use for climbing smooth surfaces.[7][10]

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.[5][7] On the undersides of the coxae and trochanters of the last pair of legs, Solifugae have fan-shaped sensory organs called malleoli or racquet organs (sometimes spelt racket). Sometimes the blades of the malleoli are directed forward, sometimes not. Neither the mode of operation nor the function of the malleoli is yet clearly understood.[4] It is suspected that they are sensory organs for the detection of vibrations in the soil, perhaps to detect threats and potential prey or mates.[7]

Males are usually smaller than females, with relatively longer legs.[8] Unlike females the male bears a pair of flagella, one on each chelicera. In the accompanying photograph of a male Solifugid, 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.[7]

Eyes

Solpugid eyes with presumably protective bristles

In some species, there are very large central eyes. They look like simple eyes or ocelli, but they are in fact surprisingly sophisticated. They can recognise forms, and are used in hunting and avoiding enemies. These eyes are remarkable in their internal anatomy; there is a suggestion that they 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.[11] In comparison to species where they are present at all, lateral eyes are only rudimentary.

Classification

Solifugae are not spiders, which are from a different order, Araneae. Like scorpions and harvestmen, they belong to a distinct arachnid order. There are about 1,065 species of Solifugae known, grouped in about 153 genera and 12 families belonging to the order Solifugae:[12]: 213 

The family Protosolpugidae is only known from one fossil species from the Pennsylvanian.

Ecology

Gluvia dorsalis eating a cabbage bug (Eurydema oleraceum)

Although Solifugae are considered to be endemic indicators of desert biomes,[4]: 1  they occur widely in semi-desert and scrub. Some species also live in grassland or forest habitats. Solifugae generally inhabit cold and wet habitats, specifically the Pacific Coast of the United States.They are found in North America.[8]

Solifugae are carnivorous or omnivorous, with most species feeding on termites, darkling beetles, and other small ground-dwelling arthropods. Solifuges are opportunistic feeders and have been recorded as feeding on snakes, small lizards and rodents;[4] 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, these chelicerae can penetrate human skin, and painful bites have been reported.[8]

Life cycle

Solifugae are typically univoltine.[4]: 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 his 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 will not feed during this time, she will try 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.[8] Solifugae undergo a number of stages including, egg, post-embryo, nine to ten nymphal instars, and adults.[4]

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, jerrymunglum,[13] 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.[14]

Solifugids and humans

A scorpion (left) fighting a solifugid (right)

Solifugids have been recognised as distinct taxa from ancient times. The Greeks recognised that they were distinct from spiders; spiders were called ἀράχνη (arachne) while Solifugae were named φαλάγγιον (phalangion). In Aelian's De natura animalium they are mistakenly mentioned, along with scorpions, as responsible for the abandoning of a country in Ethiopia. Anton August Heinrich Lichtenstein theorised in 1797 that the "mice" which 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 would stage fights between Solifugae and scorpions.[4]: 2–3 

Urban legends

Solifugae are the subject of many urban legends and exaggerations about their size, speed, behaviour, appetite, and lethality. They are not especially large, the biggest having a leg span of about 12 cm (4.7 in).[8] They are fast on land compared to other invertebrates. Their top speed is estimated to be 16 km/h (10 mph),[1] about one third as fast as the fastest human sprinter.[15] Members of this order of Arachnida apparently have no venom, with the possible exception of one species in India (Rhagodes nigrocinctus) as suggested in one study,[16] and do not spin webs.

Due to their bizarre appearance, many people are startled by or even afraid of them. This fear was sufficient to drive a family from their home when one was discovered in a soldier's house in Colchester, England and caused the family to blame the solifugid for the death of their pet dog.[17] They are non-venomous, although they are capable of inflicting a painful bite with their powerful jaws.[18]

References

  1. ^ a b "Egyptian giant solpugid (camel spider) Galeodes arabs". National Geographic. Retrieved June 10, 2011.
  2. ^ Pechenik, Jan (1996). Biology of the Invertebrates. Dubuque: Wm. C. Brown Publishers. ISBN 0-697-13712-0.
  3. ^ Warren Savary, ed. (March 26, 2009). "Introduction: what are solifuges?". The Arachnid Order Solifugae. Retrieved January 8, 2012.
  4. ^ a b c d e f g h i Fred Punzo (1998). The Biology of Camel-Spiders. Springer. ISBN 0-7923-8155-6. Retrieved January 25, 2010.
  5. ^ a b c Barnes, Robert D. (1982). Invertebrate Zoology. Philadelphia, PA: Holt-Saunders International. pp. 613–614. ISBN 0-03-056747-5.
  6. ^ Brown, Lesley (1993). The New shorter Oxford English dictionary on historical principles. Oxford: Clarendon Press. ISBN 0-19-861271-0.
  7. ^ a b c d e f Holm, Erik, Dippenaar-Schoeman, Ansie; Goggo Guide; LAPA publishers (URL: WWW.LAPA.co.za). 2010
  8. ^ a b c d e f G. Schmidt (1993). Giftige und gefährliche Spinnentiere (in German). Westarp Wissenschaften. ISBN 3-89432-405-8.
  9. ^ Filmer, Martin (1997). Southern African Spiders. City: BHB International / Struik. ISBN 1-86825-188-8.
  10. ^ Harmer, Sir Sidney Frederic; Shipley, Arthur Everett et alia: The Cambridge natural history Volume 4, Crustacea, Trilobites, Arachnida, Tardigrada, Pentastomida etc. Macmillan Company 1895
  11. ^ Beklemishev, Vladimir (1969). Principles of Comparative Anatomy of Invertebrates. Chicago: University of Chicago Press. ISBN 226041751. {{cite book}}: Check |isbn= value: length (help)
  12. ^ Levin, Simon A. (2001). Encyclopedia of biodiversity, Volume 1. 2001: Academic Press. p. 943. ISBN 978-0-12-226866-3.{{cite book}}: CS1 maint: location (link)
  13. ^ Skaife, Sydney Harold; South African Nature Notes, Second edition. Pub: Maskew Miller: Cape Town, 1954.
  14. ^ Ross Piper (2007). Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals. Greenwood Press.
  15. ^ IAAF (International Association of Athletics Federations) Biomechanical Research Project: Berlin 2009.
  16. ^ M. Aruchami & G. Sundara Rajulu (1978). "An investigation on the poison glands and the nature of the venom of Rhagodes nigrocinctus (Solifugae: Arachnida)". Nat. Acad. Sci. Letters (India). 1: 191–192.
  17. ^ "Stowaway Afghan spider kills family dog". CNN. August 28, 2008. Retrieved January 8, 2011.
  18. ^ 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.
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