Monday, July 6, 2009

Beware the Lord of Flies: Behold the Antipollinator!

Although bees and wasps (excluding hornets) are all that is industrious and good in a Home Bug Garden, not every insect is as honest about its identity or intentions. This very waspy looking fly is a bad example.

Far from being a friendly wasp, this demon from the fires below is a killer of pollinators: a Thick-headed Fly (Diptera: Conopidae: Physocephala sp.). In his book Insects, their natural history and diversity, Steve Marshall refers to conopids and their relatives as ‘Killer acalyptrates’ and with unholy delight describes how “bumblebees visiting flowers on a sunny day” are attacked by these “dipterous divebombers”. These depraved dipterons attack bees and wasps in flight, not to feed on them directly, but to leave behind an egg that will hatch into a parasitic maggot that will eat them alive from the inside out. No wonder Beelzebub is called the Lord of the Flies!

Take the time to look at this imposter closely and its infernal flyness will jump out at you. Bees and wasps have two pairs of wings, but Di-ptera have only two functional wings. The rear wings are modified into organs called halteres that help them maintain their balance when executing the sharp turns that allow them to make food of bees in flight (or feed on our blood or deposit eggs where we don’t want to know). Then there is the fixed proboscis that looks rather like the stabbing mouth of a tsetse fly, rather than the flexible tongue of bees. Finally, there are the devil-like horns instead of the graceful multi-segmented antennae of bees and wasps.

If these flies were attacking the queens of the yellow jackets and bald-faced hornets that were so common this Spring, then I would cheer them on. Every dead queen hornet is one less hive and many dozens fewer hornets at the barbie. Alas, according to Marshall, species of Physocephala are known to be parasitoids (the technical term for an insect parasite that kills its host) of honeybees and bumblebees. Let’s be bunt – they hate your flowers, fruit, and vegetables. Isn’t that always the way? All the really interesting bugs that show up are doing things you’d really rather they didn’t and not doing the things that you’d like done.

Here’s another other example of a killer fly – one that looks much more like a fly. Well, let’s be fair – it’s a bloody good-looking bug. Steve Marshall refers to these sciomyzid flies as “Snail killers”. Rather than tormenting useful pollinators, their maggots devote their deplorable de gustibus to mollusks. Well and good if only they were attacking the introduced, alien, destructors in the genus Deroceras – the totally without merit and abominable European Garden Slug. Given the current (and much appreciated) relatively wet June, these buggers will be on the slime march.
Alas, this sciomyzid is most likely interested in the harmless, even useful, aquatic lymaeid snails (see Marshall p. 417) that help keep the algae in our pond more or less in control. Does Nature really care anything at all about its balance in my garden? Of course not! What a bloody stupid question to ask. Am I the only too credulous gardener? I wonder how the Obama vegetable garden is going – forget the lead, what about the bugs? If it turns out the Secret Service is doing some late night pesticide appilcations, I may have to have a rant. Oh, who am I kidding? My first true rant is almost written.


  1. Great post! I was just looking at my aphid-encrusted meadow-rues and perennial lupins and wondering: Where are all the ladybug and lacewing predators that I welcome into the garden?

    On the other hand, there has been a wealth of bees this year, especially combatitive megachilids and bumbling bombids.

  2. Well written and very interesting!

    I feel I know and loathe these bugs already :)