One of the things I look for in spring is the Dark-Edged Bee-fly, Bombylius major, appearing in my garden. These are strange-looking insects, which look a bit like cute and fluffy brown bees with a huge long sting, flying backwards. In fact, the ‘sting’ is the proboscis (tongue) of the animal and is permanently out in a rigid, forward facing position. They cannot sting, nor can they bite you.
Depending on whereabouts in the UK you are, you might see the Dark Edged Bee-fly, or you might be lucky and see Bombylius discolor, the Dotted Bee-fly. If you are extraordinarily lucky, you might find one of the other nine species of Bee-fly to be found here, some of which are rather rare.
Whichever one you come across, however, they are not just a pretty face, but have a dark side to their lifestyle. I’ve said that they can’t sting or bite, haven’t I? So go ahead and try to capture one in your cupped hands if you want to – they are completely harmless1. But good luck with that, because though they might look slow and bumbly hovering in front of that flower or a few inches above your lawn, they are in fact remarkably zippy little things. Now you see it, now you don’t!
This one is Hemipenthes velutina, which is widespread on the western dunes of Jersey, but unknown anywhere else on the British mainland.
Adult Bee-flies are nectar-feeders and very useful pollinators. So, the dark side to these little fluff-balls? Well, when you see Bombylius major hovering over the surface of your lawn, they are probably females looking for the burrows of solitary bees. When they find one, they rather cleverly2 flick their eggs into the entrance of the tunnel in mid-flight, and the Bee-fly larvae, when they hatch, proceed to eat the bee larvae they find there.
Not all Bee-flies are parasitoids3 of ground-nesting bees, and – apart from the Bombyliids – they’re not all cute and fluffy, either. The smallest one, Phthiria pulicaria (seen here feeding on Dandelion nectar) has larvae that prey on micro-moth caterpillars, and the rest are larger, flatter, less fluffy flies, with a rather shorter proboscis. Most are parasitoids of sand wasps, one is a parasitoid of mason bees, three target moth caterpillars, and one is a hyper-parasitoid, because it preys on ichneumon wasp larvae4 which are already developing inside caterpillars.
So there you have it. This month’s Year Of The Fly post, in plenty of time for you to do a little swotting5 in time for the spring insect awakening. I hope you’ve enjoyed this little peek into the world of flies. Should you wish to know more, you could do worse than join the Dipterists Forum, where you will be welcomed with open arms!
1 Or you could use a net!
2 And extremely accurately
3 A parasitoid is an animal which lives at the expense of its host (ie, it eats it), eventually killing it. Some are extremely cleverly evolved, eating the non-essential parts first so that the host lives longer and stays fresh.
4 Ichneumon wasps are parasitoids, so anything which eats them in situ, as it were, is a hyper-parasitoid.
5 Yes, that’s ‘swotting’, not ‘swatting’. Don’t get carried away!