The next instalment explores the world of deserts. It begins in the largest, the Sahara, where the highest land temperatures have been recorded. Rock paintings depict creatures such as giraffes and antelopes, suggesting that at one point there was enough vegetation to support them. Now, such life has all but disappeared, with the exception of the cypress, whose roots find water deep underground. Since the night brings low temperatures, many of the creatures that live there are nocturnal. They include Fennec Foxes, geckos, jerboas and caracals. A scorpion is shown fighting a black widow spider. During the day, the desert belongs to the reptiles, which rely on the sun to warm their bodies. The Sonoran Desert is home to the Gila monster, one of the two poisonous lizards. By mid-afternoon, it's so hot that even reptiles must escape the sun's rays. However, some birds have developed methods for keeping cool. The sandgrouse evaporates moisture by fluttering its throat, while the road runner also uses its tail as a parasol. Plants that are best adapted to the habitat are the creosote bush and cacti, of which the saguaro is one of the biggest. The nomadic Tuareg people cross the Sahara from one side to the other - but can't do so unaided. They rely on the camel for transportation, as much as it needs them to periodically dig for water. Despite this, it is one of the best adapted desert animals: it can go without water for ten times as long as a man.