When speaking of the fastest animals in the world, it makes sense to talk about three separate groups. These are: the fastest animals on land, the fastest animals in the air, and the fastest animals in water.

Mammals are the fastest animals on land, with the cheetah, which can run 70 miles per hour (113 km per hour), taking the lead. Compare this with the fastest insect, the hawk moth, which reaches 33 miles per hour (53 km per hour) and the fastest reptile, the spiny-tailed iguana, which can reach 21 miles per hour (34 km per hour). The fastest bird on land is the ostrich which runs at 43 miles per hour (69 km per hour), while the wild turkey can attain 15 miles an hour (24 km per hour), with the chicken following at 9 miles per hour (14 km per hour).

Following the cheetah, we find a number of other mammals, including the wildebeest, lion, and Thomson’s gazelle, all of which can obtain 50 miles per hour (80 km per hour), and the hyena, zebra, and Mongolian wild ass, all of which can reach 40 miles per hour (64 kilometers per hour). The white-tailed deer, wart hog, and grizzly bear all check in at 30 miles per hour (48 km per hour). The fastest dog is the greyhound, which can run 43 miles per hour (69 km per hour), while cats can reach speeds of 30 miles per hour (48 km per hour).

In the water, fish take the lead. Sailfish are the fastest animals in the water at 70 miles per hour (113 km per hour) – the same speed in the water as cheetahs attain on land. Mako sharks can reach 60 miles per hour (97 km per hour), and marlins, 50 miles per hour (80 km per hour). The fastest mammal in the water is the killer whale, which can swim at up to 48 miles per hour (77 km per hour).

But neither insects, reptiles, mammals, or terrestrial bird speeds come anywhere close to birds in flight. Birds are not only the fastest animals in the air: they are the fastest animals on earth. Swifts can fly at 106 miles per hour (171 km per hour). Peregrine falcons fly at 90 miles per hour (171 km per hour) and dive at 200 miles per hour (322 km per hour). In other words, the short answer to the question is: peregrine falcons are the world's fastest animals.