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Budding Science

 

Solifugids

by Jonathan Leeming

 

Photo of a solifugid Solifugids are curious little creatures which due to their odd appearance have been referred to by different names including romans, sunspiders and beard cutters. They belong to the class Arachnida, which also includes spiders, scorpions, whip scorpions, ticks pseudoscorpions and harvestmen.

There 900 known species of solifugids world-wide, of which Southern Africa is richly endowed with 6 families and a total of 240 species. Solifugid comes from Latin and means 'fleeing from the sun' which is an apt description since most are nocturnal although some are diurnal. The larger species tend to be nocturnal while the smaller brightly coloured species are diurnal. They are more abundant in drier regions and range in size from 25mm to 75mm in length.

Although they may look similar to a large spider, they are different in many respects. Solifugids do not have venom or silk glands. They appear to have ten legs, but upon closer inspection the first pair of legs are not legs at all but pedipalps. The pedipalps have a sensory function, aid in feeding and have suckers at their tips to enable them to climb smooth surfaces such as glass. Their head has a very characteristic shape with powerful jaws or chelicerae with which they seize and chew there prey. The chelicerae are indicative of each species. Sexually mature male’s have backward pointing hook like structures called flagella on their chelicerae which are used in courtship. They can produce a twittering sound by rubbing their chelicerae together. The abdomen consists of 11 clearly defined segments with no pedicel (a narrow part of the body in-between the abdomen and head). Although they have two large beady, simple eyes their eyesight is poor. Situated on the first two segments of the abdomen are five pairs of special organs called racketorgans that pale in colour and perform a yet unknown function. Organs of taste, smell and hearing are situated on the feet and chelicerae. The feet are characterised by stiff hairs or spines which help them run rapidly over soft sand. The whole animal is covered by long sensory hairs or setae which glisten in the sun.

In some species retreats are located under rocks, logs and other debris which are merely scrapes in the ground which is made by loosening the soil with their chelicerae and moving it away with their feet. Other species can ‘swim’ in desert sand while others construct proper burrows. Solifugids are solitary hunters by nature and will actively seek out prey for instance spiders, scorpions, insects, small vertebrates and other solifugids. They are also opportunistic and will scavenge whenever they can. Some solifugids are specialised feeders and prey selectively on a single prey species. They have an insatiable appetite and sometimes gorge themselves until almost ready to pop. After subduing a prey item, some solifugids bite off the preys legs, then proceeds to eat it head first. They have an incredibly high metabolism and never seem to stand still for a moment. They are attracted by lights and are commonly found near campfires where they are more frequently encounted. Unlike their relatives the scorpions, they are difficult to keep and rarely live for long periods of time in captivity.

Mating takes place at the end of the rainy season. During mating the male inserts a spermatophore into the female. Depending on the species, between 20 and 200 eggs are produced which are laid in a burrow. The young emerge about four weeks later although the period is greatly influenced by external factors such as temperature. The female guards the eggs and the young solifugids until their first instar when they disperse. The young undergo direct development and after 9 instars, become sexually mature adults. Their lifespan is about 12 months depending on the species.

Solifugids exhibit interesting behaviour patterns. They are called hair cutters because it is said that if a solifugid gets tangled in hair it will cut it's way free. Although this has never been substantiated they do make nests out of animal hair and there have been reports of people and pets loosing small patches of hair due to these animals. When active during the day they avoid the hot patches of ground and run from shadow to shadow even if the shadow is made by a human. When the human moves, the solifugid moves into the shadow. This gives the impression that the animal is chasing the human thus solifugids are commonly called hunting spiders.

Although these harmless creature may seem fierce and intimidating they perform some good to mankind by keeping scorpion, spider and insect populations in check.

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