Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and grow from a hollow sphere of cells, the blastula, during embryonic development. As of 2022, 2.16 million living animal species have been described—of which around 1.05 million are insects, over 36,000 are fishes, around 11,700 are reptiles, over 11,100 are birds, and 6,596 mammals—but it has been estimated there are around 7.77 million animal species in total. Animals range in length from 8.5 micrometres (0.00033 in) to 33.6 metres (110 ft). They have complex interactions with each other and their environments, forming intricate food webs. The scientific study of animals is known as zoology.
Of the living animal species which have been described, which group has the most?
There are 1.05 million (1,050,000) insect species, which is the largest group in the animal kingdom.