Pest profile

Tachinid Flies

Tachinidae (shown: Trichopoda pennipes) · Diptera: Tachinidae[5]

Tachinids are the most important parasitic flies in biological control. Their larvae develop inside caterpillars, beetles, true bugs and other insects, and kill them.[1][2]

Feather-legged tachinid fly (Trichopoda pennipes) with an orange abdomen, black thorax and dark smoky wings on a green leaf
Feather-legged tachinid fly (Trichopoda pennipes) with an orange abdomen, black thorax and dark smoky wings on a green leaf. (c) Theo Rickert, some rights reserved (CC BY) — via iNaturalist, CC BY 4.0

How to identify it

  • Most adults are 1/8 to 1/2 inch long; many are blackish to gray, and some mimic bees or wasps.[1]
  • Abundant bristles cover the head and body, and many species look somewhat like house flies.[1][2]
  • Eggs are oval and white; on some hosts you can see them glued to the head or back.[1][2]
  • Trichopoda pennipes, a parasite of squash bugs and stink bugs, is house-fly sized with an orange abdomen, velvety black head and thorax, and a fringe of hairs on the hind legs.[3]
  • Mature larvae often leave the host and form an oblong, dark reddish to blackish pupal case nearby.[1]

Look-alikes

Look-alikeHow to tell them apart
House flyMany tachinids resemble house flies but are covered in abundant, stiff bristles.[1][2]

Where it lives

More than 1,300 species live in North America, and adults turn up in almost every habitat, resting on foliage, visiting flowers or searching for hosts.[2]

US map: public records from 49 states since 1990 (GBIF).

Biology and life cycle

Depending on species, females glue eggs onto a host, insert them into it, or lay them on leaves the host later eats.[1][2]

Larvae feed first on nonessential tissue, so the host lives normally for a while before it dies.[2]

Most tachinids overwinter as mature larvae inside a host, and many have several generations a year.[1]

Adults feed on nectar and on honeydew from aphids and scale insects.[2]

Trichopoda can parasitize up to 80% of squash bugs, though parasitized bugs keep feeding and laying eggs for a time.[3]

Damage and signs

  • They don't feed on plants. Their larvae attack caterpillars, adult and larval beetles, sawfly larvae, true bugs and grasshoppers.[2][4]

Health risk

Tachinid flies do not harm people or plants.[4]

Control

Prevention

No control is needed; tachinids are important natural enemies of many major pests.[2][1]

Biological control

Many tachinid species have been introduced into North America to suppress pests that arrived from elsewhere.[2]

Common questions

What are the small white dots on this caterpillar or squash bug?
They may be tachinid eggs; several species glue conspicuous white eggs to the head or body of their host.[2][1]
Why don't butterfly gardeners like them?
Because tachinids parasitize caterpillars, people raising butterflies may not appreciate them.[2]

Sources

  1. University of California Statewide IPM Program, “Tachinid Flies (Natural Enemies Gallery).” ipm.ucanr.edu/natural-enemies/tachinid-flies/ (accessed 2026-10-06)
  2. University of Wisconsin-Madison Extension, “Tachinid Flies.” hort.extension.wisc.edu/articles/tachinid-flies/ (accessed 2026-10-06)
  3. Cornell University College of Agriculture and Life Sciences, “Biological Control: A Guide to Natural Enemies in North America: Trichopoda pennipes (Feather-legged Fly).” biocontrol.entomology.cornell.edu/parasitoids/trichopoda.php (accessed 2026-10-06)
  4. University of Florida/IFAS Entomology and Nematology Department, “Mole cricket glossary: Tachinid flies.” entnemdept.ufl.edu/molecrickets/mcri002e.htm (accessed 2026-10-06)
  5. iNaturalist, “Trichopoda pennipes taxon page (order and family).” www.inaturalist.org/taxa/133764 (accessed 2026-10-06)

Updated 2026-10-13. Built from sourced records. Spot an error? Tell us.