The tachinid flies (family Tachinidae) are by far the largest and most important group of insect parasitic flies, with over 1300 species in North America. It is a diverse group with some resembling large or small drab houseflies, and others brilliantly colored.

All species are parasitic in the larval stage. Many are important natural enemies of major pests. Several species of tachinids have been introduced into North America from their native lands as biocontrols to suppress populations of alien pests. The female may lay her white oval eggs on the skin of the host insect, or insert the egg into the host’s body, or leave them in the host’s environment, such as on leaves, where the host will ingest them. The larvae then feed on the host tissues, causing death.

Larval tachinids parasitize caterpillars, adult and larval beetles, sawfly larvae, various types of true bugs, grasshoppers, or other types of insects. Many important pests are suppressed by tachinids.

The adult flies typically feed on pollen and can be important pollinators of some plants.