Photo: Russ Ottens, University of Georgia, Bugwood.org
Tachinid fly eggs laid on hornworm caterpillar
Photo: Charles Ray, Auburn University, Bugwood.org
People may be surprised to learn there are many beneficial flies that prey on garden pests. In fact, parasitoid flies are second only to parasitoid wasps in the sheer magnitude of pest insects they kill. There are 12 families of flies with thousands of species in which some members are parasitoids, but of these the tachinids are the most important. Most tachinids are endoparasites, which means that the developing larvae (maggots) feed within their hosts. Adult female tachinid flies employ a variety of methods to ensure their young will have ready access to food as they grow: some lay eggs on leaves to be eaten by caterpillars, others insert eggs or maggots directly into the host, and still others attach eggs or maggots to the outside of the host. Eggs consumed by the host or inserted by the mother hatch into maggots inside the victim. Eggs affixed to the skin of prey hatch and the maggots bore into the body of the host. Safely inside, the maggots complete their development, consuming their host as they grow. Who knew so many flies were doing us so much good in the garden!
Important species in Maryland: Various Tachinid spp., including Trichopoda pennipes (Feather legged fly) and Istocheta aldrichi.
Life stage(s) that feed on pests: Larvae (maggots). Adults usually feed on honeydew, nectar, or pollen, although a few species feed on host insects as well.
Pest(s) fed on: Tachinid flies most commonly parasitize the immature life stages (eggs, larvae or caterpillars, nymphs, and/or pupae) of beetles, butterflies, and moths, but also earwigs, grasshoppers, sawflies, and true bugs. Feather legged fly (Trichopoda pennipes) attacks stink bugs and leaf footed bugs, including squash bug and green stink bug. Istocheta aldrichi parasitizes adult Japanese beetles.
Eggs: Most tachinids lay small (up to 1/20” in size), oblong, white or grayish eggs.
Larvae (maggots): usually develop within the host and are not seen.
Pupae: Are commonly small, dark reddish, oblong cases.
Adults: Many resemble house flies in size and color. They have robust bodies; are usually gray, black, or striped in color; with stout, hairy bristles protruding from the tip of the abdomen. The Feather legged fly is bright orange with velvety black head and thorax; with dark legs (hind legs have a fringe of short, black hairs); yellow feet; large, brown eyes; and brown and black wings.
Where to find: Tachinid flies are found throughout the garden and landscape, and are frequently mistaken for houseflies. Feather legged fly is commonly found in the garden laying pale, oval eggs on the side of squash bugs. Istocheta aldrichi may be seen in lawns and shrubbery attaching eggs to the thorax of newly emerged adult Japanese beetles. The most obvious sign of tachinid fly activity may the presence of oblong, white eggs glued to the top of the head or body of a host insect.
How to attract and conserve: Most adult tachinid flies feed on nectar and pollen, especially from flowering umbelliferous plants such as carrot, dill, and other herbs, and composite flowers such as asters and rudbeckias , as well as other flowering plants. They will also feed on aphid honeydew, so having non-crop plants infested with aphids helps support tachinid flies.
For more on tachinid flies:
UC IPM online - Natural enemies gallery: Tachinid flies