Tachinid flies are parasites of various insect pests, including certain true bugs, beetle larvae, moths, grasshoppers, and sawflies. Adults are grey to brown flies covered with dark bristles (hairs) and a shield-like structure on top of the thorax. At 2-20 mm (1/12-4/5 inch) long they are about the size of a house fly. The white, flat, and oval eggs are typically laid externally on the head or thorax of the host insect. The larvae of tachinid flies are pale maggots that are not observed since they develop within a host.
- Tachinid flies are some of the most common flies, while also being the most important parasitic fly and an effective agent of biological control.
- Habits vary between species, but most pupate outside of the host and can sometimes be seen as a black or dark red elongated pod.
- Keeping flowering plants in the garden and avoiding the use of broad-spectrum insecticides will help maintain populations of these flies.
Adult tachinid fly on a flower. Image credits: David Cappaert, Bugwood.org
Tachinid fly and caterpillar host. Image credits: Ansel Oommen, Bugwood.org
Tachinid eggs on an armyworm. Image credits: Robert J. Bauernfeind, Kansas State University, Bugwood.org
Life history and habits
Tachinid flies have four life stages: egg, larva, pupa, and adult. The exact life cycle and preferred host depends on species. Adults feed on nectar and pollen. They are ectoparasites, i.e., they lay eggs outside the bodies of their prey, usually near the head. The eggs hatch almost immediately and the larvae burrow into their host. In most species, one larva develops inside one host, but some species can produce several larvae per host. The larvae of most species develop through tree instars and grow larger each molt. The host insect is eventually killed after larvae feed internally for a week or more. Mature larvae can also overwinter inside the host.
Avoiding the use of broad-spectrum insecticides will help conserve populations of beneficial insects. Diversifying crops and including pollen- and nectar-producing plants in gardens or near crops can help attract tachinid flies. Allowing aphid populations to persist in nearby areas can help provide honeydew and alternative sources of prey.
Cannon, C., M. Murray, R. Patterson, and K. Wagner. (n.d.). Beneficial Insects of Utah. Utah State University – Extension. Available https://extension.usu.edu/pests/files/pubs/Beneficial-Insects-of-Utah-ID-Guide.pdf
UCIPM. (n.d.). Tachinid Flies. University of California Agriculture and Natural Resources. Available https://ipm.ucanr.edu/natural-enemies/tachinid-flies/