The larvae of moths in the family Geometridae (the second largest family of moths in North America) are known as loopers, inchworms and spanworms. These names are derived from the looping gait of the caterpillars. They generally have only two or three pairs of prolegs (at the hind end) rather than the usual five pairs of most moth and butterfly larvae. The lack of prolegs in the middle of their body causes them to move by pulling the hind prolegs up to the true legs on the thorax in the front of their body, thereby forming a loop, and then extending the body forward.
Many Geometrid caterpillars evade predators by flinging themselves from trees and dangling by a silk thread that is attached to the tree at the other end (see photo). After the danger passes, they climb back up the silk and return to their leaf-eating.