The English word "desert" derives from the Latin for "abandoned", but the notion that deserts are devoid of life is simply wrong. Plants, insects and animals have all become finely-tuned to desert environments over the centuries, sometimes in astonishing ways, evolving devices that allow them to survive in places where other creatures would simply perish. These devices range from the simple (the extraordinarily large foot pads of the Namib's desert elephants, enabling them to cross long stretches of dunes between oases) to the minutely complex (the Saharan jerboa's ability to survive without drinking).

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At opposite ends of Africa, the Sahara and the Namib are very different deserts, sharing only high aridity and rapid fluctuations in temperature. The Sahara is the largest desert on earth, bigger than Europe, but only about 15% sand. The Namib is a relatively narrow strip of land, more than 2000km long but only a few hundred wide, consisting of some hardpan and huge amounts of sand, including the world's highest dunes. The Sahara is among the driest places on the planet (despite occasional savage thunderstorms). The Namib is dry too (it hardly ever rains) but, as a coastal desert alongside a cold ocean current, it is fog-prone; many living things have evolved to capture that moisture from the air. The Sahara is a new desert (less than 12,000 years old). Parts of the Namib are more than 80 million years old; it is possibly the oldest continuous desert on earth.

At the Gobabeb Research Institute in the Namib, scientists have for years been cataloguing and studying the wildlife. They talk with a proselytising zeal about the dazzling array of creatures they have found and their idiosyncratic adaptations to the extreme heat and dryness. They showed me a tiny scarab beetle that had learned to irrigate its "landholdings", excavating tiny furrows at a constant gradient to channel condensation. On the dunes we found a fog collector beetle, which stands on its forefeet with its back to the drifting mist, condensing it into tiny runnels leading to its mouth. Other marvels included a lizard that hops from foot to foot to diffuse heat absorption, a beetle that curls into a ball to roll down dunes to conserve energy and a spider that spins a small cone-shaped web to attract and condense dew. Namib geckos stay alive by licking their own eyeballs, on which water condenses.

Plants, too, are perfectly attuned to desert life. One of the Namib's shrubs has learned to exude salt, which then extracts moisture from the air and feeds it back to the plant. Namibia's national plant, the Welwitschia mirabilis, which though linked genetically to pine trees is ancient enough to share some of the characteristics of primitive mosses, can live with minuscule amounts of water.

Individual plants can grow to two metres, but they never have more than two leaves per plant. Even in the absence of moisture the leaves just keep on growing, albeit at a glacial pace. Moderate-sized welwitschias have been carbon-dated to about 1000 years; some of the larger ones are probably much older. When the rare rains come, a welwitschia can grow almost as rapidly as grass. One of the most resilient desert plants is the acacia, endemic to the Sahara and Namib, which has evolved both tap and lateral root systems to maximise its search for water. The tap root descends to extraordinary depths. The most famous specimen marked an ancient caravan route from the salt mines at Bilma to the city of Agadez in the Aïr mountains. This "Tree of Ténéré" is celebrated in Tuareg legend as the first growing thing sighted by travellers returning from the deep desert. The only tree for 225km, it grew in stony soil with no water in sight. When it was finally knocked over by a drunken truck driver, its roots were traced down to 40m.

The thorny mimosa shrub has similarly deep roots, as does the prolific tamarisk, prized for the shade of its dense foliage.

Most of the desert's creatures are small, with dull colours and moderate water requirements. They live in burrows or holes, emerging only at night. Insects such as scarab beetles, dung beetles, scorpions and small rodents are the commonest. The jerboa, an inquisitive rodent that looks half mouse and half tiny kangaroo, is found deep in the Sahara, mostly in Algeria and Libya. It can sometimes be spotted hopping through a camp at night, "running" on its hind legs and using its long tail as a rudder, making sharp banking turns midair.

It survives the scorching heat in closed sand burrows, where it can stay for days at a constant 76 °C. It is one of the few mammals that never drinks; the nomads say it reabsorbs its own moisture, and indeed there are indications that the jerboa can actually recycle the moisture from its own exhalations.

The jerboa's greatest enemy is the fennec fox, a ferocious creature, even at a weight of two pounds. Its range is similar to the jerboa's and it too spends its days underground in a burrow, sometimes 10m long. Its huge ears radiate heat and its fur-soled feet protect against the burning sand. It eats rodents and roots, from which it derives moisture.

The small sand cat also tunnels, spends daytime underground and preys on the jerboa - as well as venomous snakes, which, combined with its disconcerting habit of erupting from hidden burrows like some spectral jack-in-the-box, fills Tuareg nomads with superstition. Its large spreading feet enable it to cross soft sand easily and its acute hearing detects ultrasound, allowing it to locate underground prey with astonishing accuracy. Another staple of its diet is the Saharan gundi, which lives in a large part of the central Sahara. Gundis actually seem to like the heat: in winter they spend much of the day sunbathing on warm rocks. Confronted by a predator (usually a snake or a lizard) the little rodent plays dead, lying motionless on its side with its legs stretched out, not breathing for up to a minute.

A few predators maintain a precarious existence in the rocky massifs of the central Sahara. Once, at dusk in Niger's Taghouadji mountains, our party heard a harsh screaming from the rocks above. The Tuareg were unfazed. "Caracal," one said. In the morning we scrambled up to find tracks in a sandy patch. The paw prints were huge, suggesting a beast the size of a lion. "No," said one of the Tuareg, "1.5m at most, including tail." "Are they dangerous?" I asked.
"To us?" He looked surprised. "No. To birds and jerboa, small things only." He'd seen a caracal just once, he said, in the early dawn, on a dead run after some hapless prey, but he'd heard they were capable of taking a low-flying bird in flight. "The most dangerous things here are much smaller: things that get into your robes at night." He meant snakes and scorpions.

Snakes inhabit many parts of the Sahara apart from the hottest and most arid sand seas, although their overall numbers are small. The Saharan horned viper is the commonest, along with its close cousin, the sand viper. There are also cobras in Egypt and puff adders, white-bellied carpet vipers and kraits in southern Mauritania and Mali. The deadly horned viper strikes its prey from hidden sand burrows, erupting suddenly and sinking its fangs into a jerboa or a passing ankle. The Namib's snakes have also evolved devious strategies for catching prey. Peringuey's adder camouflages itself to look like the debris in which insects forage; the Cape cobra has learned to feign death, lying in the open sun looking desiccated until an unwary rodent crosses its path. Scorpions are a more pervasive problem in all deserts. Prudent travellers are careful when turning over a stone and always peer under their pillow before retiring. A scorpion sting is invariably painful, though not always fatal. Like the spitting cobra, some of the Namib's species are capable of blinding humans by squirting poison into their eyes.

The most exhilarating of all desert animals, perhaps because of their scarcity and natural grace, are the antelope. Many species inhabit the fringes of the Namib, including gemsbok, eland and springbok. A few antelope species are still found in the Sahara.

Some Mendes antelope survive in Egypt and in high parts of the desert, as does a small population of Dorcas gazelles (placed on the Endangered Species List in 1980). The Dorcas, only 60cm high at the shoulder, lives primarily in the Sahel and in parts of Arabia, though it has been found far into the Sahara's interior (it can survive for long periods without water and may even live its entire life without drinking). It can run for miles at high speeds (over 45kph), reaching over 90kph when panicked.

Most impressive, however, are the fleet-footed addax, the Sahara's largest mammal. They have been spotted 135km from the nearest water, travelling over rough terrain at over 60kph. Elegant animals with white coats, dark faces and spiral horns, a metre tall at the shoulder, addax are found only in isolated spots.

The Tuareg tell many stories about the addax. They are supposed to sense desert grasses and bushes from afar, and, because grass is linked to water, a wise man watches the addax. The nomads of the Sahara, like the San of the southern deserts, came to learn desert behaviour many centuries ago by studying the wild creatures that live there. Science is still learning.

OASIS WILDLIFE

As pit stops go, you can't beat an oasis for style. With towering, picture-postcard palm trees and green, shaded pools, oases are the ultimate in R&R for the weary and wayward, not to mention the waterless. Just as humans seek the shelter of these lush islands of flora among shifting, sun-baked dunes and rocky escarpments, so too do desert-dwelling animals.

Some of the world's largest and most plentiful oases lie in southern Tunisia, sandwiched between its famous salt lake, the Chott el-Jerid, and the Eastern Erg, one of the Sahara's greatest sand seas. They shelter a variety of highly adapted creatures, from rare foxes and comic rodents to graceful gazelles. Spring-fed pockets of vegetation blooming in the wadis (riverbeds), the oases provide colour in this otherwise bleak landscape, together with the last remnants of Tunisia's prehistoric acacia savannah. Many rare breeds have been successfully reintroduced here, including the elaborately maned Barbary sheep (Africa's only wild sheep); the addax (once prized for its meat and beautifully spiralled horns); the elegant scimitar-horned oryx (creatures so lovely ancient Egyptians kept them as pets) and Africa's largest gazelle, the long-limbed Dama.

Daytime temperatures can soar to 45 °C in the shade, sometimes making water scarce. At these times, many desert animals extract moisture from desert scrub and foliage, browsing a selection of wild herbs that reads like the appetiser menu of a fine restaurant: Italian cress, wild rocket, violet cabbage. Some, such as the oryx, employ strategies such as nibbling on vegetation at night, when it contains up to 75% more water. Others, like the addax, are simply built for endurance. A network of blood vessels at the base of the animal's skull cools the blood flowing to the brain, keeping it 2-3oC below the rest of its body temperature and enabling it to withstand the punishing sun for hours.

Daytime siestas and dispelling heat are keys to survival for animals further south. The tourist retreat of Ksar Ghilane, a shady stretch of palm and tamarisk trees 75km south-east of the desert town of Douz, is also the terrain of the fennec fox and the Dorcas gazelle. An excursion by camel is the best, and in most cases the only, way to see Jebil NP, where high dunes make motor travel impossible, even by 4x4. This low impact approach also increases the odds of seeing wildlife, which would otherwise likely disperse at the far-off sound of revving engines.

Three Desert Safaris
Libya: Exodus, www.exodus.co.uk, has a 16-day Sahara tour exploring Roman ruins, prehistoric rock art and desert, from £1385 per person.

Namibia: Skeleton Coast Safaris, www.orusovo.com, operate five day fly-in safaris visiting the towering dunes of Sossusvlei, the Skeleton Coast, Huab Valley and Kunene River, from US$2585 per person.

Morocco: Travelbag Adventures, www.travelbag-adventures.com, offer an eight-day desert adventure from Marrakech across the Tizi-n-Tichka pass to Ouarzazate and on through the desert via Zagora, from £399 per person.