Flies for Thanksgiving

A pair of Leafminers (Liriomyza sp.) celebrate Spring in the Home Bug Garden

Thanksgiving is a time for giving thanks for many things; but historically, a good harvest has to rank near the top. In the Home Bug Garden the harvest is what the hail, drought, floods, frost, slugs, pathogens, birds, and bugs have left for us to eat. Of all of these kleptoparasites and vagaries of the weather, the bugs steal the least. The caterpillars of the Cabbage White Butterfly devastate my kohlrabi and kale. Flea beetles and root worms prevent me from growing broccoli, turnips, and radishes. Leaf miners make chard, beets, and spinach unprofitable use of limited space. But most other insect 'pests' don't do enough damage to make a difference. I suppose that is one advantage of gardening in the cold, short growing seasons of Zone 3.

House Sparrows do more damage to peas in the HBG than leafminers

The pair of mating flies at the top may be one of those minor HBG pests, perhaps the same fly that makes leaf mines in my peas. But unless I use row covers, the House Sparrows eat most of the young peas leaves, so pea leaf-miners are rather rare and more interesting than pesky. These particular Leaf-mining Flies (Agromyzidae) belong to the very large genus Liriomyza which contains many of the important agricultural pests. The family itself is very successful - the third largest family of acalyptrate flies according to another of my reasons for giving thanks today: a new book by Steve Marshall: Flies, the Natural History and Diversity of Diptera (2012, Firefly Books) and the time to peruse it. And not just agromyzids, but 10 other families of Diptera have maggots that munch through the middle cell layers of leaves.

Lauxania shewelli Pérusse & Wheeler, 2000

Maggots munch dead leaves to, as demonstrated by another highly successful family of acalyptrates (i.e. 'higher' Diptera with an organ called a ptilinum but without calypters) the Lauxaniidae. Like many Diptera, the larvae of Lauxania shewelli Pérusse and Wheeler, 2000, feed on decaying matter. I'm not sure exactly what detritus Lauxania maggots feed on, this is often the case when a fly has not come under close scrutiny for eating us or our livestock or our plants, but many lauxaniid maggots have the interesting habit of mining dead leaves. Adults scrape spores and mycelia of fungi from live leaves (Marshall 2012), probably what is going on in the picture above. As Steve Marshall points out, adult flies are not known for eating leaves - they seem to never have managed that evolutionary leap.

Scathophaga cf stercoraria (Linnaeus, 1758) predator as adult, saprophage as maggot

So we have numerous maggots that find leaves, dead or alive, perfectly acceptable as food, but no adult flies with the ability to eat vegetation. I find that curious. Many flies, like the Golden Dung Fly Scathophaga cf stercoraria (Linnaeus, 1758) above, are predators of insects that piece and suck their haemolymph. Far too many flies have the ability to suck our blood. But adult flies don't eat leaves or suck the sap of plants, unless it is oozing from a wound. I guess that is something else to give thanks for.

Lecanocerus compressiceps Borgmeier, 1962

Well, there is the caveat that we don't actually know what all that many flies do. Take the Scuttle Fly (Phoridae) above, Lecanocerus compressiceps Borgmeier, 1962. Unfortunately, the common name 'Antler Fly' is already taken by some fascinating little flies that feed only on the discarded antlers of moose and deer and a strange fruit fly from New Guinea. The generic name 'Lecano-cerus' seems to mean 'plate-horn', which is descriptive, but hardly evocative. I'm sure these male ornaments are used for something interesting, but google and Marshall both fail when it comes to explaining just what. Yet another mysterious fly! Well, nothing so interesting seems to be on the wing at the moment and I'd better do something with all those harvested tomatoes before they turn into dew-loving flies. So Happy Thanksgiving to all my Canadian readers!

A plate-horn to the genus author, but an Albertan Antler Fly to me