EPOW - Ecology Picture of the Week

Tachinid (Parasitic) Fly, unknown species, Family Tachinidae
Congo River Basin, Africa

Explanation:  We all instinctively swat flies.  But here is one fly that does us good.  

This is a parasitic or tachinid fly, a member of large insect family Tachinidae. Tachinid flies are found most everywhere; I photographed these specimens while on expedition in swamp forests in the heart of the Congo River Basin in central tropical Africa.  Tachinid flies generally lay their eggs on other insects.  The tachinid larva then hatches, burrows into, and feeds upon its host internally, eventually killing it.  In so doing, tachinid flies help to keep many pest species in check.  

At least among the 1,300 species of tachinid flies of North America, many lay their eggs on caterpillars of harmful moths or on larvae of pest sawflies, beetles, or other insects.  In fact, a number of tachinid flies have been introduced or imported into the United States as biological control agents to suppress introduced pests such as Douglas-fir tussock moth, western hemlock looper, sawflies, gypsy moths, browntail moths, and satin moths, which are tree defoliators.   They can even be good in your garden!

An unidentified native tachinid fly of the Congo.

Some tachinids lay eggs on plants sought by their host species.