Solifugae

Solifugae Fossil range: Late Carboniferous–Recent PreЄ Є O S D C P T J K Pg N
A male Galeodes (from R. A. Lydekker, 1879)
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Arachnida
Subclass:	Dromopoda
Order:	Solifugae Sundevall, 1833
Families
see text

Solifugae is an order of Arachnida, known as camel spiders, wind scorpions or sun spiders, comprising more than 1,000 described species in about 153 genera. They may grow to a length of 7 cm (2.8 in), and have a body comprising an opisthosoma (abdomen) and a prosoma (head) with conspicuously large chelicerae, which are also used for stridulation. Most species live in deserts and feed opportunistically on ground-dwelling arthropods and other animals. A number of urban legends exaggerate the size and speed of Solifugae, and their potential danger to humans.

Anatomy

Unidentified solifugid, Arizona

Solifugids are moderate to large arachnids, with the larger species reaching 7 centimetres (2.8 in) in length. The body is divided into a forward part, cephalothorax or prosoma, and a ten-segmented abdomen or opisthosoma. The prosoma comprises the head, mouthparts and somites containing the pedipalps. It is divided into a relatively large anterior carapace, including the animal's eyes, and a smaller posterior section.^[1][2]

The most distinctive feature of Solifugae is their large chelicerae, which are longer than the prosoma. Each of the two chelicerae are composed of two articles forming a powerful pincer; each article bears a variable number of teeth.^[1][2]

While solifuges appear to have ten legs, they have eight legs like other arachnids; the first set of appendages are pedipalps, which function as sense organs similar to insects' antennae and give the appearance of an extra pair of legs. The pedipalps terminate in eversible adhesive organs, which are used to capture flying prey, and for climbing. They stridulate with their chelicerae, resulting in a rattling noise.^[3]

Of the four pairs of legs, the first pair are smaller in size, and act as accessory tactile organs used to feel the animal's surroundings, so that only the other six legs are used for running.^[2] On the last pair of legs, Solifugae have fan-shaped sensory organs called as racquet organs or malleoli.^[1]

Like pseudoscorpions and harvestmen, they lack book lungs, having instead a well-developed tracheal system that takes in air through three pairs of slits on the animal's underside. In some species there are very large central eyes that are capable of recognising forms, and are used for hunting. Lateral eyes are only rudimentary, if present at all. Males are usually smaller than females, with longer legs.^[3]

Classification

Solifugae are not true spiders, which are from a different order, Araneae. Like scorpions and harvestmen, they belong to a distinct arachnid order. There are about 1065 species of solifuges known, grouped in about 153 genera and 12 families belonging to the order Solifugae:^[4]:213

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

Ecology

Gluvia dorsalis eating a cabbage bug (Eurydema oleraceum)

Solifugae are considered to be endemic indicators of desert biomes;^[1]:1 most Solifugae inhabit warm and arid habitats, including virtually all deserts in both the Eastern and Western Hemispheres, but excluding Australia.^[3] Some species have been known to live in grassland or forest habitats.

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;^[1] Solifugae have even been videotaped consuming lizards. 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.^[3]

Life cycle

Solifugae are typically univoltine.^[1]: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, depending on the species: she guards 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 centimetres (2.0 in) has been observed to eat more than 100 flies during that time in the laboratory.^[3] Solifugae undergo a number of stages including, egg, post-embryo, nine to ten nymphal instars, and adults.^[1]

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, jerrymuglum, sun scorpion and sun spider. In southern Africa they are known by a host of names including red romans, haarskeerders and baardskeerders, the latter two relating to the belief they use their formidable jaws to clip hair from humans and animals to line their subterranean nests.^[5]

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.^[1]:2–3

Urban legends

An unidentified solifugid against a ruler, marked in inches

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 perhaps 12 centimetres (4.7 in).^[3] They are fast on land compared to other invertebrates, the fastest can run perhaps 16 km/h (10 mph), nearly half as fast as the fastest human sprinter. Members of this order of Arachnida apparently have no venom, with the possible exception of one species in India (see below) and do not spin webs.

In the Middle East, it is widely rumored among American and coalition military forces stationed there that Solifugae will feed on living human flesh. The story goes that the creature will inject some anaesthetising venom into the exposed skin of its sleeping victim, then feed voraciously, leaving the victim to awaken with a gaping wound. Solifugae, however, do not produce such an anaesthetic, and they do not attack prey larger than themselves unless threatened. Other stories include tales of them leaping into the air, disemboweling camels, screaming, and running alongside moving humvees; all of these tales are false.

Due to their bizarre appearance many people are startled 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 death of their pet dog on the solifugid.^[6] The greatest threat they pose to humans, however, is their bite in self-defense when one tries to handle them. There is essentially no chance of death directly caused by the bite, but, due to the strong muscles of their chelicerae, they can produce a proportionately large, ragged wound that is prone to infection.

Venom

While the absence of venom in Solifugae was long thought a fact,^[3] there is a single published study of one species, Rhagodes nigrocinctus, carried out in India in 1978 by a pair of researchers who did histological preparations of the chelicerae, and found what they believed to be epidermal glands.^[7] Extracts from these glands were then injected into lizards, where it induced paralysis in 7 out of 10 tests. While this study has never been confirmed, and while other researchers have been unable to locate similar glands in other species, this particular species does appear to possess venom, although it is not known if there is any mechanism for introducing it into prey.

References

External links

• Weygoldt, Peter (1969). The Biology of Pseudoscorpions. Harvard University Press. ISBN 0674074254. 
• Mikkelson, Barbara & David P. "Camel Spiders" at Snopes.com: Urban Legends Reference Pages.
• "Camel Spiders: Behind an E-Mail Sensation From Iraq". National Geographic. June 29, 2004. http://news.nationalgeographic.com/news/2004/06/0629_040629_camelspider.html. 
• "The Arachnid Order Solifugae". http://www.solpugid.com/index.htm.