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.