The order Solifugae belongs to the class Arachnida. It is a fairly large order with about 240 described species from 147 genera and 6 families. Solifugae constitute an abundant, diverse and successful group of animals. As predators they are of extreme importance in regulating potentially harmful insects.
COMMON NAMES
The Solifugae are known in South Africa by a variety of common names. The Latin word solifugid means "fleeing from the sun". Although many species are nocturnal, some are active during the day earning them the name "sun spiders". They are very agile animals and swift when fleeing, resembling small balls of thistle blown by the wind over the sand and as a consequence they are also known as "wind spiders". Because they have the tendency to avoid heat they tend to run from shadow to shadow. Frequently the shadow of man is also chosen, causing great concern, since this gives the impression that they are giving chase. This behaviour has earned them the name "jaag" or "jag spinnekop" (wandering spiders). In some parts of South Africa they are also known as romans, derived from the word "rooiman" (red man) owing to the striking reddish-brown colour of some species. In some regions they are called "vetvreters" (fat eaters). This is due to their feeding behaviour to gorge on available food, so much so that they can hardly move afterwards.
Probably the most common name used throughout the country is "haarskeerders" (hair cutters) or "baardskeerders" (beard cutters). This is based on the belief that should a solifugid become entangled in a girl's long hair, it will cut its way free. However, no scientific evidence exists to support this notion. Other speculations are that the hair is cut by females of some species to use as lining for their retreats. Some evidence for the latter has been found.
MORPHOLOGY
Most of the common names give the false impression that these animals are spiders, which is not true. Like spiders they have eight legs and belong to the class Arachnida (animals with eight legs) but here the similarity ends. They differ in size, general morphology and behaviour. Two important differences are venom and silk glands, which are absent in the solifugids. The solifugids have large heads, which contain the large and powerful chelicerae or jaws and the muscles needed to work them. It is said that solifugids have the most formidable pair of chelicerae in the animal world. Each chelicera consists of two segments or fangs. The fangs have strong teeth, which like the blades of shears, move against each other in a vertical plane. The prey is held and passed to and fro through the chelicerae with the help of the pedipalps until it is chewed to a soft pulp. While chewing the whole front part of the body moves in rhythmic motion. There are no internal venom glands or ducts and the bite of a solifugid is not venomous, only painful because of its severity. They are also able to produce a kind of twittering sound with their chelicerae when spines are rubbed together. The chelicerae of the male carry an elongated structure (the flagellum) dorsally which might play a role during mating. Each species of solifugid has a uniquely shaped flagellum.
They have two black eyes situated close together on a slight tubercle on the front of the head. The abdomen has no pedicel like that of spiders and it consists of 11 clearly defined segments. The abdomen is soft and can easily extend, enabling them to eat large portions of food. During pregnancy the increase in the abdomen is remarkable and the stretched membrane seems almost at bursting point. They appear to have five legs but the first pair of appendage is the pedipalps, which are very strong and used for varied functions such as fighting, mating, feeding, drinking and climbing. The pedipalps are covered with very long hair, with suckers at the tip, which enable them to climb smooth surfaces. The suckers are so strong that they are able to support their body weight. When drinking the tips of the pedipalps are held together and placed in the water, bringing the liquid to the mouth like a pair of hands.
The first pair of legs is usually thin and short. They are not used for walking but are stretched out in front and used as additional tactile organs. The fourth pair of legs is the longest and strongest and carries strange white structures known as racket organs on the first two segments. The function of these organs is still uncertain. The whole body is covered with long, silky sensory hairs up to 50 mm in length. When viewed in full sunlight they sparkle in the sun.
BEHAVIOUR
The sun spiders are solitary animals with a strong antisocial nature. They live in retreats scraped out of the sand under rocks and logs. They use their chelicerae to loosen the substrate and by using their whole front body like a bulldozer they are able to move large amounts of soil around. These retreats are used for resting, ecdysis and the deposition of eggs.
They will defend themselves voraciously against their enemies. They prey on other solifugids, spiders, scorpions, insects and even reptiles like geckos and lizards. Because of their lack of venom they use speed and their strong chelicerae to attack immediately. Solifugae are usually seen during the hot season while looking for food. Searching for food involves random running and searching for prey. Prey is detected by tactile and visual stimuli. Some species are exclusively predators of termites and they all play an important role in the control of these insects.
They have also been observed to prey on dead animals e.g. birds. The chelicerae were used to cut the soft feathers close to the bird's skull. After a large area was cleared of feathers, the solifugid started feeding on the head, crushing the skull to get to the brain.
Solifugae can be divided into two groups depending on whether they are active during the day or night. The larger solifugids are usually active at night and spend most of the daytime in their burrows. After dark they emerge in search of prey and are frequently attracted by light, both electrical or campfire. During the rainy season they are often enter houses having been attracted by the light. The species that are active during the day are usually smaller in size and more brightly coloured. They are usually seen during the heat of the day, darting from bush to bush in search of food and shade.
During mating the male deposits a spermaphore in the vagina of the female. The number of eggs produced varies between species, from 20 to 200. The eggs are deposited in a burrow and usually hatch within three to four weeks. The newly hatched embryos are translucent and immobile. Solifugae live for about one year and go through nine instars before they reach maturity.
