Tachinid Fly – Gymnosoma fuliginosa

Tachinid Fly – Gymnosoma fuliginosa
Order Diptera / Family Tachinidae

This species is a known parasite of stink bugs in Pentatomidae: Clorocroa, Eurygaster, and Euschistus
Tachinid Fly - Gymnosoma fulginosa
Tachinid karma: this fly has itself been parasitized by another insect – see the tiny egg pasted to its abdomen?
Family Tachinidae has been studied extensively and many of their parasite-host interactions have become well-known and exploited in commercial biological control of many crop pests. All known tachinid fly larvae are parasitic on other arthropods, almost exclusively on other insects [1].

Thaddeus William Harris, M.D., a noted American naturalist and entomologist, published the first host record for the Tachinidae in 1841. Harris was a close friend of Nicholas Marcellus Hentz  (1797-1856), himself a pioneering arachnologist. Harris practiced as a physician at Milton Hill, Massachusetts until the 1830's, when he followed his father's footsteps and became the Librarian at Harvard. In 1831, he was appointed a commissioner  for a botanical and zoological survey of Massachusetts, and he would produce a catalog of the insects in that state, listing an astonishing 2,350 different species [2,3]. 

Subfamily Phasiinae is among the most primitive of the tachinid flies. They lack a uterus, or ovisac, that allows for storage of eggs undergoing embryonic development. They deposit their undeveloped (unembryonated) eggs either directly onto the skin or partially or completely insert them inside the host. Eggs maturing on the outside of the host remain vulnerable for several days and are subject to removal by the host or are lost when the bug molts.

However, the vast majority of Tachinidae use a strategy employing eggs that have completed much of their development inside their mother prior to deposition – such eggs are ready to hatch quickly so that the larvae can gain protection by burrowing into the host. (Some hatch so quickly it was thought the flies were positing live maggots.) Females employing this method are capable of storing  hundreds or thousands of eggs in a range of development, spitting out the mature ones from the distal end of her ovisac-conveyor belt.

Many other species broadcast tiny eggs onto plant substrate already damaged by host caterpillars – such eggs gain entry to the host by being ingested, somehow managing to slip past the chewing mouthparts to be "activated" by digestive juices to penetrate the host through the gut wall. Thousands of these eggs are broadcast only on plants specific to the required host. A variation used by most of the Tachininae leaves eggs in places mostly likely to be visited by victims; the larvae wait in ambush, protected from desiccation by a sclerite suit of armor. They attach themselves and burrow into the host as soon as one blunders into range [1].

Tachinid Fly - Gymnosoma fuliginosa
This species is a known parasite of stink bugs in Pentatomidae genera Clorocroa, Eurygaster, and Euschistus  [4]

Tachinids utilize at least eight orders of insects as hosts; Lepidoptera larvae probably support the largest number of species, esp. in the large subfamilies Tachininae and Goniinae. Flies in subfamily Phasiinae most often parasitize true bugs in Hemiptera such as stink bugs, leaf-footed bugs (below), seed bugs and damsel bugs [1].

Beetles are not immune to Tachinid depredation. Both adults and larvae of Scarabidae (scarab beetles), Cerambycidae (longhorned beetles), Elateridae (click beetles; larvae are called wireworms), Carabidae (ground beetles), Chrysomelidae (leaf beetles) are all victimized by fly larvae that have developed an impressive array of armaments for penetrating the tough, chitinous exoskeleton of the Coleoptera. Even some weevils are attacked, their larvae are vulnerable while burrowing. Insects in Orthoptera, Mantidae, Dermaptera, as well as Diptera larvae of Tipulidae and Tabanidae all serve as hosts.

Leaf-footed bug (Coreidae) with undeveloped tachinid egg cemented to its pronotum 


  1. D.M Wood, Manual of Neararctic Diptera Vol. 2, Tachinidae
  2. The Kouroo Contexture, "People mentioned in (Henry David Thoreau's) 'The Maine Woods' "
  3. Archives, Gray Herbarium Library, Harvard University Herbaria, "Harris, Thaddeus William"
  4. Paul Henri Arnaud, U.S. Science and Education Administration, California Academy of Sciences, "A host-parasite catalog of North American Tachinidae (Diptera)"
Flies of North America – Order Diptera. Flies are prevalent in virtually all habitats, with over 16,000 species in North America. Flies can be distinguished from all other insects in that they only have one pair of normal wings. Most flies have compound eyes and mouthparts adapted for piercing, lapping or sucking fluids.
Syrphidae | Flies Index | Tachinidae | Bee Flies | Robber Flies