50. Pipunculidae – big head

I hope I can be forgiven a degree of self-congratulation at having reached the, albeit arbitrary, milestone of having now seen and identified 50 dipteran families this year. Fifty is about where I thought I might get to for the whole year, and yet there is plenty summer left. Of course with every addition it gets harder to find a new family and so the plateau may be getting closer, but for the moment I award myself a moment of quiet satisfaction. †

To return to reality, my lax sweeping technique was again highlighted by my failure to catch flies that dipterists beside me were pootering up with ease. The scene was Fallin Bing near Stirling, once the waste heap of the Polmaise coal mines, now a pyramid of flowers and adolescent woodland. My desultory sweeping and individual fly stalking technique was not very effective. The secret I am told is that the more air you pass through your net, the more flies you will catch. That’s a nice way of saying put your back into it, so I got to work and very quickly was rewarded with this goggle-eyed prize. No family key is needed to recognise one of these “big-headed flies” for the eyes occupy almost the whole of the head – although of course I did run it through just to check.

The other notable feature of these flies is that once caught, killed, and pinned, the heads tend to fall off. So I am equally pleased with myself in being able to post a picture of an intact fly. Just look at those eyes! There isn’t much to see on the dark stumpy body, but the wings are vast compared to the rest of the fly, and the veins produce a pleasingly varied set of cell-shapes – long and thin, long and broadening, wide and narrowing to a sharp tip, blunt-ended, sharp-ended, completely enclosed. Flies of the British Isles quotes Verrall’s praise for the family from British Flies Vol VIII (1901): “the Syrphidae may be the grandest, but the Pipunculidae are the most exquisite, hoverers in the Diptera, as they can hover easily in a folded net, between the folds,without touching the network.”

A key to the genera from the Pipunculidae study group places this fly in the genus Pipunculus, but after that it gets harder, especially for the ladies which this is with its fierce ovipositor intended for hemipterous bugs. Fine legs too, ending up with those neatly-shaped tarsi – a head-turner of sorts!

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