This programme discusses insectivores. Shrews are descendants of the earliest mammals, which were scurrying creatures that had a diet of insects. Their warm blood enabled them to hunt at night while dinosaurs slept; they nurtured their young and gave them milk. When the dinosaurs died out some 65 million years ago, the mammals' inherent features meant that they could proliferate. The shrews evolved: the elephant shrew is shown, alongside its prepared pathway of getaway routes; while others adapted further into species of mole. The increased relative size of armadillos came about because they broadened their diet. Other animals grew larger owing to more of their favoured nutrition being available: these include the giant anteater and the pangolin. However, Attenborough hails the evolution of the bat — a winged mammalian insect catcher that can navigate using echolocation — as being "magical". The European brown long-eared bat switches off its echolocation and then uses its keen sense of hearing to detect an insect's location through its movements. He ascends 3 kilometres into the night sky over Texas to investigate why there should be so many bats at such a height. It transpires that this is also heights to which moths from the Tropics climb up as they migrate. Whereas the bats in Texas are forced to migrate in winter, Attenborough visits a cave in Canada where they stay all year round and go into deepest hibernation when the cold weather arrives. In New Zealand, bats seem to have reverted to the hunting techniques of their ancestors, and are shown tackling a weta on the ground.
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