leaf insect, common name given to herbivorous insects of leaflike appearance forming a single family in the order Phasmida. Leaf insects are green and have extremely flattened, irregularly shaped bodies, wings, and legs; they are usually about 4 in. (10 cm) long. Their wings often have venation similar to that of the leaves on which they live. The eggs of leaf insects are scattered on the ground and hatch in the spring. The young resemble the adults except for their smaller size and reddish color; shortly after they begin feeding on leaves they turn green. Leaf insects are tropical in distribution. The walking sticks of tropical and temperate climates are members of the same order. Leaf insects are classified in the phylum Arthropoda, class Insecta, order Phasmida.