Monday, August 24, 2009

Thick-headed Flies

Conops quadrifasciata pairs remain together like this for some time after mating has taken place, and take to the air in unison

Females have a more slender abdomen that's sharply curled under at the tip

The exceptional width of the male's head is visible here. Maybe it's because the female's vision is obscured by the male above, so he has to act as look-out for both of them

These flies, mimicking wasps and linked together during mating in characteristic biplane arrangement, as thick-headed flies Conops quadrifasciatus that I found in a field of ragwort in Durham. The bottom photo shows the broad head which gives these insects their common name. They’re parasites of bumblebees, laying eggs on the adult bees which are then literally eaten alive by the parasitic larvae. One study carried out in Switzerland and published in 1990 found that almost 35 per cent of workers of early bumblebee Bombus pratorum and common carder bee B. pascuorum sampled in August contained this parasite’s pupae. At this time of year there are always a lot of sleepy-looking bumblebees apparently resting on flowers and showing little sign of feeding, and many of these are likely to be suffering from parasites, including conopid fly infestations. There’s no doubt that habitat destruction has been a major factor in bumblebee decline, but it’s also true that parasite infestations can have a very significant impact on local populations too.


  1. Superb quality,Phil. They`ve blown me away!!!

  2. Superb close up shots, Phil. Quite an unusual looking fly. I have seen several weary looking bumblebees around the lavender bushes so I wonder if those flies are here somewhere.

  3. Thanks Dean, it was one of those rare occasions when the insects were really accommodating and allowed me plenty of time to get the angles right and check all the camera settings.... and there was no wind to sway the plant that they'd settled on

  4. Thanks John, I've noticed a lot of 'sleepy' bees around here recently. I though it might have been the weather, but now I'm inclined to think that they're weakened by parsites.

  5. Thanks Keith, they're fascinating insects and this was the first time I'd really looked at them closely