Monday, August 12, 2013

A bumblebee's worst nightmare?

The arrival of these mating thick-headed flies, which I think are probably Conops quadrifasciatus, is very bad news for bumblebees nesting in our garden. They're parasites, whose larval stages feed on the body fluids (haemolymph) and ultimately on the internal organs of their bumblebee hosts.

Female thick-headed flies spend much of their time on flowers, waiting for bumblebees to approach, then they grab them - often while the bee is still in flight. They have specially-adapted reproductive structures on their tails which prise apart the hard segmental plates of the bee's exoskeleton, so that they can insert an egg through the softer tissue in between. As many as a third of worker bumblebees in a colony can be parasitised and there is some evidence that even in the early stages of infection the behaviour of the bees is affected, so that they spend more time collecting nectar for their own consumption and return to the nest less frequently.

There are plenty of published accounts of the way in which Conops lays its eggs in its host but in a quick search of Google images I couldn't find any of the parasite attached to, or laying its eggs in the host either when they were at rest or in flight - it seems to happen quickly and would be something that anyone would be lucky to see, let alone photograph.

It's a tough life being a worker bumblebee: if you're lucky you work from dawn until dusk all your short life; if you are unlucky you meet Conops.............


  1. Even after four years following your posts half the time I'm little wiser. These are horrid almost as bad as humans....whoops Homophobics. I'll get there Homo sapiens. It will take me years yet but it's an enjoyable journey. Thanks again.

  2. Thank you for the information, I didn't know about these horrible things and am now fearful for my bumble bee nests which have given me much enjoyment and seem to have been much busier this year than I have seen before.

  3. Hi Adrian, soon after I posted this I did see one of these flies land on a bee - but only for a second - probably not long enough to lay an egg

  4. Hello Ellen, You don't need to worry too much - bumblebees have coexisted with these flies for millennia and it's unlikely that they'll wipe out whole colonies and they can't get at the queens. They do have a gruesome life style though. They are most common in late summer.

    1. Thanks Phil, that is reassuring.....I have been developing a wildlife friendly garden over the last two years to combat most of my neighbours concrete and Gnome ones, and particularly liked the insect house you made from Hog Weed stems....I'm collecting some to try to do the same.