Something I spotted from Peter Chandler’s spreadsheet of records from the Dipterists Forum field meeting was that there are quite a few families that are, to the innocent eye, just varieties of fungus gnats. The 1980 Royal Entomological key to the Mycetophilidae by Hutson, Ackland and Kidd mentions seven subfamilies, of which four are now considered as families in their own right (Bolitophilidae, Diadocidiidae, Ditomyidae and Keroplatidae), only the latter of which I had found so far.
My feelings about fungus gnats so far have been, initially pleasure at adding another family to my list, then appreciation of their distorted morphology with a hunched, almost apologetic thorax and tiny head in combination with enormously extended legs with poke-your-eye-out bristles, and lastly a relief at not having to tangle with any of their five hundred species again. This aversion was reinforced when I saw how the expert Dipterists dealt with their fungus gnat catch at the field meeting – they simply gave their specimens to Peter Chandler who identified them in production line mode using the vast key stored in his head. But if I was going to make it to bus-pass age numbers on my fly family challenge I would have to become braver, so I set off to get gnats.
At this time of year the woods are heaving with all sorts of nematoceran flies – crane flies, mosquitos, midges and gnats, a flystorm raining upwards from the disturbed undergrowth so that a few sweeps of the net resulted in a flutter of long-legged prisoners, most of whom could be safely ignored – I was after smaller prey. The haunts of gnats are damp hollows, rotten logs, muddy margins and so I crept about in all the dark corners of the woods, sweeping a tiny harvest with my net and pooter as the combine worked in the fields above. Back at the microscope I surveyed the catch which, as expected, were mostly Mycetophilidae, the largest family of fungus gnats. When you look at them closely they turn out to be subtly varied with a hint of character, wing spots, quirky bristles, shyly strutting their stuff – maybe I will come back to them yet.
Did you spot that the wings of last one are much less crowded with veins – there is a wide area of open wing at the base (a cell) and heading from it towards the wing tip a forked vein between two stronger veins – this is the hallmark of the family Diadocidiidae, and since there are only three British species I pressed on and am fairly sure that it is Diadocidia spinulosa. The larvae apparently live in mucous tubes under rotting logs, possibly associated with crust-forming and bracket fungi. Of the 40 previous records on NBN, there are none between one from the Black Wood of Rannoch, contributed by Peter Chandler, and a couple from Cumbria from a previous Dipterists Forum field meeting, no doubt also identified by him. I feel in august company.