The First Flies of Spring

Easter weekend was the first real sign of Spring 2009 in Edmonton – warm enough for a few insects that had overwintered as adults (or pupae ready to emerge) to take to the wing. Although the eye is naturally drawn to the larger and more brightly coloured individuals, e.g. the Milbert’s Tortoiseshell butterflies (Aglais milberti) that have consistently shown up in early mid-April for the last three years or the ladybird beetles that overwinter in the mulch and leaf litter, a host of smaller and less obvious animals come out to enjoy the early spring sun. Prominent among these are the flies.

One of the most diverse orders of insects, but one that is rarely celebrated, is the Diptera or two-winged flies. If you want to know the identity of a fly, then it helps to have a friend that knows their flies (we are lucky to have several such friends). It also helps to have a pinned (but not wriggling) specimen, because the sad fact is that many insects cannot be identified except by close microscopic examination. However, if you are trying to grow a Home Bug Garden, then it seems perverse to kill the insects that live there (mosquitoes, perhaps the least loved of all Diptera, excepted).

So, except when some arthropod pays the ultimate price, identifications on this blog will be tentative ones based on photographs or observations. Take all such names with a grain of salt and remember that the higher the taxonomic level, the more likely the identification is to be correct. Thus, family names will usually be correct, genera less so, and species least of all.

As I was saying, the sunny Easter weekend lured out a few flies of more than passing interest and we were able to add two families to our Home Bug Garden records: a member of the family Lauxaniidae (possibly a species of Sapromyza) and two species of shore flies (Ephydridae): one a member of the genus Paydra (sometimes known as fat-faced flies) and the other possibly of Ephydra (or a related genus). All three of these flies are tiny and inoffensive. The larvae (i.e. maggots) of the lauxaniid may mine leaves, but unlike the pesky agromyzids that make a mess of my columbine, beet, and pea leaves, lauxaniids mine dead, decaying leaves (see p. 416 in Marshall 2006). The larvae of the shore flies feed on microbes in wet spots – probably the decaying vegetation in our pond or bog. So these flies are actually helping the garden by releasing nutrients otherwise tied up in decaying vegetation and microbial biomass.

Larger and more problematic are the blowflies. Probably everyone has seen members of the Calliphoridae (blowflies, bottle flies, screwworms), whether they realize it or not. The bodies of these flies often have a green, blue, or coppery metallic sheen and they are very common around humans because the maggots generally feed on flesh, often carrion (including the dead meat we like to throw on the barbecue), but sometimes in living flesh as is the case with the screwworm. Actually, like the shore flies, the maggots of many calliphorids are more interested in the microbes than the meat, which is the reason they are useful for cleansing festering wounds in Maggot Debridement Therapy. This is true of the Northern Blowfly (Protophormia terraenovae), a carrion fly that is also useful to CSI types that need to estimate the time of death.

I suspect one reason that carrion flies are common in the early spring in northern climes is that when the snow melts, the animals that failed to survive the winter become available for consumption. Some spring ephemeral plants take advantage of the flies that are attracted to carrion for pollination. For example, the red flowers and fetid odour of Stinking Benjamin (Trillium erectum) appear to mimic red, rotting meat and are pollinated by a variety of flies that are attracted to carrion.

If you’d like to learn more about Diptera, or indeed any other group of insects in North America east of the Rocky Mountains, then I highly recommend Steve Marshall’s magnificent Insects. Their Natural History and Diversity.