Myopa testacea

N London - as the wings were expanding, this sac-like structure was everted from the head! What can it be?

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shane58 says:

I'm sure I've read somewhere what this is but cannot for the life of me recall it.
could it be a weak spot exposed by pressure in the body?
Posted 15 months ago. ( permalink )

tristanba says:

that would figure Shane, as the body must be under pressure as fluid is pumped into the wing veins
Posted 15 months ago. ( permalink )

apparently this membranous sac is called the ptilinum - it is pumped up with haemolymph in order to aid emergence from the pupal case. After emerging, the fluid and the sac is retracted back in the head and the muscles controlling it degenerate.

Many thanks to Bugs for Thugs, an entomology blog I stumbled across!
Posted 15 months ago. ( permalink )

shane58 says:

nice one Tristan!
wonder if any of them have a red sac? this would be a great image for red nose day! it's a ugly fly BTW but a great shot as always!
Posted 15 months ago. ( permalink )

tristanba says:

ugly? - Shane I'm surprised at you...
Posted 15 months ago. ( permalink )

shane58 says:

must be having an off day - in retrospect, the pasty face and nose sac are actually endearing features! ;0)
Posted 15 months ago. ( permalink )

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Taken with a Canon EOS 20D.
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Taken on April 8, 2008

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Myopa testacea

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shane58 says:

tristanba says:

tristanba says:

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