a locust

Of all the animals found in the deserts, insects are the most numerous. Insects are members of a group of organisms known as arthropods, which also contains arachnids (scorpions, spiders, solifugids, mites and ticks), crustaceans (crabs, lobsters and woodlice), and myriapods (centipedes and millipedes). Representatives of all these groups live in the world's deserts.

True insects and arachnids have a hard waxy outer layer, which is waterproof and allows very little water loss due to evaporation. This is an obvious advantage where temperatures are high and water is in short supply. Woodlice, centipedes and millipedes, on the other hand, do not have this feature but are also able to survive admirably in deserts, often by burrowing into the sand during the hottest parts of the day.

Some desert insects can fly, but the ability of others can be poor or non-existent. Flight allows them to cover great distances in the search for food and water. Among the flying insects in the deserts are locusts. Although individually they are fairly unremarkable, they can group together in enormous swarms covering as much as 1,000 square kilometres, and they can destroy crops at an alarming rate. Other flying insects in deserts include flies, wasps, butterflies and moths.

Among the flightless insects that abound in desert regions are earwigs, termites, ants and beetles. Some of the most remarkable of these are the honey pot ants, which take advantage of the sudden occasional spurts of ephemeral plant growth brought on by the erratic desert rains. Confronted with an excess of nectar, these ants nominate some of their workers to act as living storage jars, which are then fed huge amounts of nectar until their bodies swell to several times their normal size. These special ants then feed the others in times of shortage.

Scarab beetles feed on the dung of desert animals such as camels and goats, which they roll into balls and bury in the ground. The predatory carabid beetle shelters from the sun during the day, but emerges at night to hunt.

Despite their hard casing, insects are still vulnerable to the desert's extremes. Because of their small size water loss is a serious problem, and relatively few insects spend long periods on the surface during the day. Many desert insects burrow into the sand where the temperature remains almost constant, and it is common for insects to stay there until darkness falls. However, some beetles that stay on the surface use their long legs to keep their bodies as far away from the hot sand as possible.

Scorpions are among the best adapted creatures to the arid environment. Although they have a very low rate of water-loss, nearly all desert scorpions are nocturnal, spending their days in burrows or under rocks. Scorpions are carnivorous and have pincers with which to seize their prey while they administer a deadly poison from the sting in their tail. Their main diet consists of insects and spiders, but they will sometimes kill other scorpions, particularly if they are in a small place. Scorpions rarely drink, obtaining most of the fluids they require from their prey. Despite their fearsome reputation, scorpions are shy creatures and few of them are dangerous to humans.

Desert spiders tend to be large in order to minimise loss of water through their surface. Because of the lack of vegetation in many parts of the desert, there is little opportunity for web building, so most desert spiders hunt on the ground. They avoid the heat by burrowing or taking cover under rocks, emerging at night to seek out their prey. Many spiders are camouflaged to escape from larger desert predators. In the Sahara wolf spiders and jumping spiders are common, although there are a wealth of other species to be found, many of them still unidentified.

Similar to spiders and scorpions, and sharing characteristics of both, are the solifugids or camel spiders. Spending most of the day in burrows, they can measure up to 12 centimetres across, and feed on insects, spiders, scorpions, small mammals, lizards and birds. Like scorpions, camel spiders can endure extreme temperatures for long periods, and rarely drink.

Woodlice, centipedes, and millipedes are all found in deserts, and the Sahara has its fair share. Woodlice do not have the waterproof outer layer possessed by insects and arachnids, but nonetheless are able to withstand desert conditions well. Centipedes and millipedes typically have a large number of legs and no waterproof outer layer. Centipedes can grow up to 20 centimetres long and have poisonous claws to subdue their prey. Millipedes are less widespread than woodlice and centipedes in the Sahara, being less well-adapted to the desert environment. Successful desert millipedes tend to be large.

photo courtesy of WWF-UK

Exploration | Tropical rain forests | African deserts | Desert insects | On the Line home page