squash bug, name for a true bug, Anasa tristis, found throughout the United States and S Canada. It damages squash, pumpkin, and related plants by sucking the juices from leaves and stems. The adult is dark brown and measures about 2/3 in. (16 mm) long. The eggs are laid in the late spring and hatch in two weeks. The green larvae, or nymphs, soon turn brown or gray. Birds feed on both nymphs and adults, but the most effective natural enemy is the larva of a tachinid fly, which develops within the body of an adult or larval squash bug, feeding on and eventually killing the host. The squash bug is classified in the phylum Arthropoda, class Insecta, order Hemiptera, and family Coreidae.