While most species are phytophagous, many are predacious, or fungivores, or are parasitoids. They live in rainforest canopies, the driest deserts, in lakes, and above treeline on mountains. In one sense the most unusual property of beetles is not some aspect of their structure or natural history, but their sheer number. There are more known species of Coleoptera than any other group of organisms, with over 350,000 described species. Perhaps the most famous quote about beetles comes from the great population geneticist J.B.S. Haldane, who was asked what might be learned about a Creator by examining the world.
Beetles are holometabolous insects, normally with adecticous, exarate pupae.
Most species have chewing mouthparts. There is a gula present on the undersurface of the head. The four living suborders of beetles diverged from one another in the Permian and early Triassic, and are substantially different from one another. Adults differ in the structure of the prothorax, hind wing, abdomen, ovary, testes, and so on. The major differences are summarized in a table .