Tarsier

The tarsier is descended from ancestors that were active in daylight and lost the reflective layer (tapetum lucidum) that helps other nocturnal animals see in the dark. When tarsiers became nocturnal again, they could not re-evolve that mirror, so instead they evolved gigantic eyes to gather as much of the little available light as possible. Each eyeball is around 16 millimetres across and weighs more than the animal's entire brain — proportionally the largest eyes of any mammal. The trade-off is that the eyes are so large they completely fill the sockets and cannot move, and the tarsier compensates by rotating its head about 180 degrees in each direction, like an owl, to look around.

It is the only primate known to eat an entirely animal diet, with no fruit, leaves, gum, or other plant food at all. Its staple is insects — beetles, crickets, grasshoppers, cicadas, moths — and larger species also take spiders, small lizards and snakes, roosting birds, and even bats snatched in flight. Other primates such as galagos, some marmosets, and chimpanzees eat significant amounts of animal prey, but all of them also eat plants. The tarsier's specialisation is reflected in its simple gut, its forward-facing hunting eyes, and its huge ears, which it can furl and unfurl to pinpoint the rustle of an insect.

Tarsiers are extremely difficult to keep, and stress is a genuine and well-documented problem. They are small, nervous, nocturnal specialists that need live insect prey and space to leap, and in confinement they may leap repeatedly into mesh or walls and injure their heads, or stop eating. There are widely reported accounts of captive tarsiers dying after being handled, exposed to camera flashes, or kept in noisy, brightly lit tourist enclosures, and some "tarsier sanctuaries" that allowed close contact were criticised for high death rates. A few conservation facilities, notably in Bohol in the Philippines, now keep them in large semi-wild enclosures with no handling, and this works far better. The blunt version — do not pick up a tarsier — is essentially correct.

Very far for its size. A tarsier is a "vertical clinger and leaper" — it perches gripping an upright sapling or stem with its long fingers and toes, which have expanded adhesive pads at the tips, then springs off using its greatly elongated hind limbs and ankle bones (the tarsal bones that give the animal its name). Jumps of 3 to 5 metres between trunks are routine, and some sources cite longer. In mid-flight it rotates its body so that it lands feet-first and upright against the next vertical support, ready to jump again, and it uses its long tail as a counterbalance and brace.