Fly with large hole in abdomen

[Bruce Williams]

Stony Stratford, Bucks. 20th November 2009.

The fly seemed unconcerned and flew off shortly after this pic was taken. Any ideas what might have caused the hole (I'm assuming it isn't natural?). Help with id also appreciated:



Bruce

[Wild-Woman]

Blimey, you do find the strange ones Bruce. Well spotted. Looks like the exit hole of something but I would've thought that would spell the end of the fly. Can't help you otherwise but I'll follow this thread with interest.

[JRsbugs]

Nasty, I doubt it would have lived long. It looks the same as the other fly with the suspect larva in the spiracle which is not anything but a spiracle.

This was nearly 4 weeks after the other fly, could it be it was one of several hatched at the same time, this having the parasite/s in the abdomen which has/have now left? Or could it be the same fly, where the parasite made it's way in through the spiracle down to the abdomen, had completed it's cycle and come out the abdomen.

The hole looks very neat so it seems there had been some sort of capsule stuck on the outside. So, did the parasite enter from the capsule, or did it make it's way in elsewhere, eat the contents then pupate on the abdomen after chewing a hole out?

Just had another look at the spiracle on this fly, it looks to be very sunken around it but I can't see it well.

[Bruce Williams]

Appreciate your interest Jules .

Janet - The two flies were were found at different locations about 20 miles apart. However I agree with your general speculation on what might have caused the hole - it is remarkably clean and uniform in appearance isn't it.

Bruce

[Dogghound]

Im guessing its the exit wound made by a hymenopteran (note the neat roundly cut hole) of some description. Very strange as they almost always end up feeding on the vital inturnal organs before emerging.

[JRsbugs]

Bruce.. the front legs on this one are grey too, not sure if that can happen with ageing but they are both similar flies in the family Anthomyiidae of which there are plenty.

The timing might be a clue, both flies might have been parasitised with the same species or similar parasite. I haven't a clue as to which it might be, but Hymenopteran as Dogg suggests looks the most likely. Thinking of those which attach themselves to the underside of Ladybirds, leaving the vital organs intact, there must be more that do the same but in this case it might have left without the main meal. Perhaps the parasite got eaten!

I'm sure I've come across parasites entering the body then making their way down to the abdomen, can't say what though. The Chalcid wasps which parasitise Aphids then pupate underneath come to mind too.

[Bruce Williams]

Dan and Janet - interesting and thought provoking comments - thanks guys .

Bruce