The oldest beetle fossils are about 265 million years old. Since then, their numbers have increased to 350,000 known species, but there's no telling how many more are out there that haven't been discovered.

Beetles have done well by adapting to different environments. They live nearly everywhere on the planet from the dampest, hottest jungles to the driest deserts. The only place they don't live is Antarctica.

Some beetles can trap moisture under their wings, so when they travel to deserts, they bring their own water with them. Others can stay underwater, living off the air they trap under their wings. They also come in many sizes from the size of a pinpoint to nearly as large as 6 inches long.

When classifying insects, beetles fall into the group, or order, called Coleoptera (pronounced co-le-OP-ter-ah). That term comes from the Greek words coleo (sheath) and ptera (wings). The top pair of beetle wings, called elytra, serve as hard casings that protect the delicate hind wings and body below. To fly, the forewing—or elytron (singular for eltyra)—is opened enough to allow the hind wings to unfold and function.

Sources: Tree of Life, University of Arizona; graphic by David R. Maddison, University of Arizona.