tachinid fly (tăk´ənĬd), common name for any of the flies of the family Tachinidae, which parasitize caterpillars, beetles, grasshoppers, and other insects. Tachinid flies are generally small (about the size of houseflies), often bristly, and sometimes brilliantly colored. There are nearly 1300 North American species. The female typically lays her white oval eggs on the skin of the host insect, though the eggs of some species are inserted in the host's body, and the eggs of others are left in the host's environment, as for example on leaves, where the host will ingest them. The larvae feed on the host tissues, causing death. Tachinid flies are widely used as a means of biological control of insect pests. Some tachinid flies are themselves parasitized by certain wasps (see ichneumon fly). Tachinid flies are classified in the phylum Arthropoda, class Insecta, order Diptera, family Tachinidae.