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Solifuges are small spider-like arachnids that are typically associated with arid habitats with little vegetation. The approximately 1100 known solifuge species (Harvey 2002, 2003) mainly inhabit tropical and subtropical desert regions of Africa, Asia, and the Americas, but some species are also found in dry grasslands (Brookhart and Brookhart 2006). Most species are essentially crepuscular (active at dusk and dawn) or nocturnal, although some are active during the hotter parts of the day, presumably explaining the common name "sun spider". Among other common names, solifuges are also known as wind scorpions, a reference to their impressive sprinting ability, and camel spiders, a reference to the prominent arch-shaped plate on the dorsal surface of the cephalothorax of many species. Solifuges have a pair of enormous jointed pincer-like chelicerae ("jaws") which project in front of the animal between the pedipalps. The pedipalps themselves are elongate and leg-like in form. They are primarily tactile in function and are often extended in front of the body, where they are tapped on the substrate when the animal is searching for prey or (in the case of males) mates. Although they lack claws, the pedipalps have an adhesive sucker, or "palpal organ", which facilitates the grasping of prey and can even be used in climbing. Like other arachnids, solifuges have four pairs of legs, but the first pair of legs are generally reduced in size and function mainly as tactile structures. (Punzo 1998 and references therein; Brusca and Brusca 2003)
Solifuges are ferocious predators, feeding on other ground-dwelling arthropods as well as small lizards, snakes, and rodents. All or nearly all species lack venom, in lieu of which they simply tear apart their live prey with their powerful chelicerae. Some solifuges construct burrows in which they spend much of their time when not hunting or mate-searching and others hide under stones or in crevices. Females of some species guard their eggs and young offspring, which are at first gregarious but soon take on a solitary existence (sometimes after first snacking on a few siblings). (Punzo 1998 and references therein; Brusca and Brusca 2003)
Although mating has been observed in just a few species, the following likely describes the general pattern. Before copulation, the male seizes the female. In some species, he strokes and palpates her, bringing her to a passive state. He then bends her abdomen upward and opens her genital orifice with his chelicerae. Next, he produces a sperm-containing spermatophore, picks it up with his chelicerae, deposits it in her genital orifice, and leaps away. This entire sequence takes just a few minutes. In some solifuges, sperm transfer is direct, although there is still precopulatory behavior and the male inserts his chelicerae into the female orifice before and after sperm transfer. The female deposits 50 to 200 eggs in burrows in the ground or in other protected areas. (Barnes 1987) Hruskova-Martisova et al. (2010) investigated mating behavior in two sexually cannibalistic solifuges. In one species, Gluvia dorsalis, forced copulation appeared to be the only mating strategy, whereas in the other solifuge studied, Galeodes caspius subfuscus, males engaged not only in coercive mating that caused injury to their mate, but also in courtship behaviors that induce an immobile state prior to copulation (stroking with pedipalps) and during copulation (stroking and tapping). The authors suggest that coercive mating in solifuges may have evolved as an anti-predation strategy, given that sexual cannibalism occurred in around 40% of all sexual interactions observed.
Solifuges are unfortunately probably best known to the general public as the focus of alarming (and false) urban legends about them, as described here.