Although some flies are responsible for transmission of disease most are extremely beneficial. We know from fossilized specimens that insects were living 400 million years ago. The head, thorax, and abdomen of insects are formed from groups of fused segments. Insects are the first animals with the capability of flight and some scientists think that wings probably originated from insect gills. Shortly after the development of wings, about 330 million years ago, an explosion of insect species is seen in the fossil record, documenting the spread of insects into new habitat types.
Today there are insects inhabiting almost every major ecosystem in the world except the oceans .
Bugbios by Dexter Sear is a comprehensive site about everything insect, including photos, descriptions of the different insect groups and links to pages on insects and human society. 3D Bugs is a fun animation page with realistic insects from Virginia Tech. Requires free VRML download to run. Butterflies of North America is a USGS link with photos and descriptions of common butterflies and links to butterflies in other states.