Sunday, 7 December 2008
The flies are back in town
You know that summer's on its way when the buzz of blowflies fills the air.
Because it is active at lower temperatures than other flies, the native blowie Calliphora stygia is one of the first species to make its presence felt around house and garden. Calliphorids lay their eggs on all types of decaying matter — they are especially fond of corpses, visiting early and often — after which they wander over food, crockery and kitchen bench tops.
This might be why they are so fastidious when it comes to hygiene. Who know what was on that plate?
Calliphora stygia is also responsible for fly strike on sheep. Although it doesn't appear to initiate the problem, it certainly takes advantage of damage done by other species. Fortunately, there aren't many sheep around here.
Fly identification is a pain in the neck for the non-specialists (ie almost everybody I know). Calliphorids are calyptrate flies — each wing has a lobe (calypter) at the base that covers the haltere on its side. Three groups of large calyptrate flies regularly pop into gardens: Calliphoridae, Tachinidae (March or horse flies) and Sarcophagidae (flesh flies). The first two can be tricky to tell apart. If you can get close enough, you can separate them on their antennae. In calliphorids, the aristae are feathery (plumose), whereas in Tachinidae, they're not. Usually. But there are exceptions.
I said fly identification was a pain in the neck.
The insect people at CSIRO Entomology have put together a wonderful interactive atlas of fly anatomy to assist with working out which bit is which. Recommended for those with broadband.
The antennae are the structures projecting from the front of the face between the eyes. Each antenna is made up of several elements, of which two are the most obvious — the bulky flagellomere 1 and thread-like arista. In calliphorids, the arista is feathery. (See images below for a clearer view.)