Saturday, May 17, 2008

A Flesh-Fly, family Sarcophidae

I am an amateur naturalist trying to discover everything living in my garden.

Photo 1 shows a fly I found sunning itself on my bird-table late last summer.

I have no expertise when it come to fly-identification. With the help of the very nice colour plates in my copy of Insects (Michael Chinnery, Collins) however, I'm fairly certain my fly is a member of the Sarcophidae family of so-called Flesh-flies.

In general, identifying flies down to species level is a job for the experts. Page 27 of this book (The Sarcophagidae of Fennoscandia and Denmark, Thomas Pape), partly available online, gives you a flavour of what's involved. Dipterists spend a lot of their time looking at genitalia (!) -that of flies being an important aid to species recognition. I didn't subject my fly to the indignity of this, so can't be confident about its species, though from the book above a guess might be Sarcophaga carnaria (can anyone confirm or correct this?)

There are some 120,000 species of fly (Diptera), with 15,000 occurring in Europe. Chris Thompson's Diptera site contains a wealth of information, including specifics on the Sarcophagidae.Flies are distinguished from other insects in part by having only two wings, their hind pair having shrunk down to vestigial 'stumps' called halters.

There are some 2600 Sarcophagidae flies, about 300 occurring in Europe (this site lists them) and about 60 in Britain. As the name Flesh-fly implies both adults and larvae (maggots) are often associated with carrion, though in fact there is considerable variation in feeding habits across species: some concentrate on small corpses (this site has some closeups of an adult feasting on a dead caterpillar); some larvae are parasites of other insects; some predate snails, others earthworms; some species are able to live on a purely vegetarian diet. Sometimes of course, Flesh-flies become associated with human corpses. As a consequence the Sarcophagidae have been well studied by the science of forensic entomology which aims to get information about the time of a person's death by the rather grisly process of analysing any insects infesting the corpse.

The Sarcophagidae are viviparous (=females give birth to live young, the larvae). This book (Natural Enemies of Terrestrial Molluscs, G.M. Barker) explains this as an adaption to give the flies a speed advantage when it comes to getting their their young established on an ephemeral food item such as a corpse as rapidly as possible.

A final question I am left with is what purpose it serves my fly to sport the "zebra-like" black and white stripes on its back. Can anyone enlighten me?

2 comments:

R2K said...

I once killed a fly on a school bus as a kid, and tiny little maggots were inside. They all were crawling around the dead fly body. It was pretty strange to me, I didnt know what they were at the time. Somehow I thought there were these organs inside the body that were still moving.

Anonymous said...

Thank you for this info. I just killed a flesh fly that was on my curtain and discovered when I opened the tissue I had caught it in, lots of live, squiggling maggots. Both disgusted and fascinated, I had to go online to learn more about this unique fly. I had not idea that flies could bar live young.