katydid, common name of certain large, singing, winged insects belonging to the long-horned grasshopper family (Tettigoniidae) in the order Orthoptera. Katydids are green or, occasionally, pink and range in size from 11/4 to 5 in. (3–12.5 cm) long. Katydids are nocturnal and arboreal; they sing in the evening. The males have song-producing, or stridulating, organs located on their front wings. The females chirp in response to the shrill song of the males, which supposedly sounds like "katy did, katy didn't," hence the name. The song serves a function in courtship, which occurs in late summer. The female lays eggs in the ground or in plant tissue; the eggs hatch in spring. Newly hatched katydids resemble the adults except for their smaller size and lack of wings. Katydids are common in the E United States and are also found in the tropics. They are classified in the phylum Arthropoda, class Insecta, order Orthoptera, family Tettigoniidae.