It has been estimated that half of all animal species alive today are beetles; using a conservative estimate of the number of animal species, there would be at least three million beetle species on the Earth. The Coleoptera also includes some of the largest insects, like the living Hercules beetle, Dynastes hercules, shown here.
Coleoptera means "sheathed wing;" beetles have two pairs of wings, but the first pair has been enlarged and thickened into a pair of hard sheaths, or elytra, that cover the delicate hind wings. Because the elytra are fairly hard structures, beetles have a better fossil record than many other insect groups do; the oldest fossil beetles are Permian. Below is a much later fossil beetle, from the Pleistocene-age McKittrick Asphalt of southern California, a fossil-bearing tar deposit very similar to the more famous La Brea tar pits in Los Angeles (scale bar is marked in millimeters).
Because beetle elytra may be common fossils in Pleistocene deposits, they are often important sources of data on Pleistocene environments.
Our thanks to the National Museum of Natural History, Smithsonian Institution for making the stag beetle and many other fine images available on their FTP image file.
The Coleopterists' Society has information of interest to anyone interested in beetles, as well as many links to beetle-related sites. For more information on the phylogeny and diversity of the Coleoptera, try the coleopteran pages on the Tree of Life exhibit at the University of Arizona.
An excellent exhibit on the ecology of one beetle, the endangered Salt Creek tiger beetle from Nebraska, is available from the University of Nebraska Insect Ecology home page.