Tachinid Fly – Gymnoclytia sp.

Tachinid Fly – Gymnoclytia sp.
Order Diptera / Family Tachinidae

Phasiinids are among the most primitive tachinids; they deposit undeveloped eggs onto their hosts.
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Tachinid Fly

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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.

Another strategy shared by the vast majority of Tachinidae involves 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 [1].

Tachinid Flies mating

Many tachinid 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

Tachinids patronize 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, seed bugs and damsel bugs [1].

Beetles are not immune to Tachinid depredation. Both adults and larvae of Scarabidae, Cerambycidae, Elateridae, Carabidae (ground beetles), and 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. Hymenoptera alone among the large orders appears to have escaped the tachinids' attention.


  1. D.M Wood, Manual of Neararctic Diptera Vol. 2, Tachinidae
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. The other pair has evolved into small ball-like structures called halteres. Most flies have compound eyes and mouthparts adapted for piercing, lapping or sucking fluids.
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