Tachinid Fly – Gymnosoma fuliginosa

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].

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.