Scientists have identified more than 1.5 million animal species, ranging from microscopic organisms to the largest creatures ever to exist.
Animals are broadly classified into vertebrates and invertebrates, with invertebrates making up the vast majority of species.
Mammals range enormously in size, from tiny bats to blue whales weighing nearly 200 tons.
There are more than 10,000 known bird species, from the tiny bee hummingbird to the flightless ostrich.
Insects make up more than half of all known animal species, playing critical roles in pollination and food chains.