It is the larval form of long, winged insects. An antlion digs one of these funnel-shaped pits by flipping soil up and out with its head. The antlion then waits at the bottom of the pit with only its large jaws exposed. Then, when an ant or some other small insect happens to wander into the pit, the antlion grabs it with its jaws.
Antlions are actually the larval forms of large, winged insects that resemble dragonflies.
This site has scads of info, including pictures, quicktime movies of antlion behavior, and a guide to antlions in mythology, literature, and popular culture. The Io Moth Caterpillar can get to be very large and is found on many different kinds of trees and plants. Because of its multi-colored wings, the adult form of this insect is named after one of the moons that orbits Jupiter. The pale green caterpillar can grow up to two and one half inches long. These caterpillars are often found eating the leaves of many different kinds of plants, including corn.