The flies in this family are parasitoids, i.e., the females lay their eggs on or in the bodies of other insects, and when the fly larvae hatch, they gradually consume the host until it dies, and the fly larvae pupate. Many tachinids attack larval moths and butterflies, although some species parasitize other insect groups (e.g., cucumber beetles). The adults often resemble large houseflies but have a more bristly adomen.
Adult tachinid flies. Note bristly abdomen.
They sustain themselves on nectar and pollen, and so are often found on flowers during the summer.
Beneficial of the Month material courtesy of NMSU ACES:
Pocket Guide to the Beneficial Insects of New Mexico