Tachinid Flies: Tiny Parasitoids That Control Garden Pests

Often mistaken for house flies, tachinid flies (family Tachinidae) are among the most important yet unrecognized beneficial insects in the garden. These small (under ½ inch), bristly, gray or black flies are parasitoids—their larvae develop inside and ultimately kill host insects, providing powerful natural pest suppression.

How They Work

Female tachinids lay eggs on or inside host insects—primarily caterpillars, beetle larvae, and true bugs. Some species deposit eggs on foliage for hosts to ingest; others inject eggs directly into the host’s body. The hatching larva feeds internally, avoiding vital organs until its final instar, then kills the host and pupates. Adults feed on nectar and pollen, contributing to pollination, especially at higher elevations where bees are scarce.

Notable Garden Species

• Voria ruralis – parasitizes cabbage looper caterpillars.
• Lydella thompsoni – targets European corn borer; introduced repeatedly for biological control.
• Myiopharus doryphorae – attacks Colorado potato beetle larvae.
• Trichopoda pennipes (feather-legged fly) – parasitizes squash bugs and stink bugs.

Encouraging Tachinid Flies

Plant a diversity of small-flowered herbs and wildflowers (such as cilantro, dill, fennel, Queen Anne’s lace, and sweet alyssum) to provide nectar for adults. Avoid broad-spectrum insecticides. Tolerate some pest presence—it sustains the parasitoid population. Tachinid flies are not commercially available, but a pesticide-free, flower-rich garden will naturally attract them.

These inconspicuous flies are a cornerstone of biological control, silently reducing pest outbreaks while asking nothing more than a few blossoms and a poison-free environment.