26. Scatopsidae – terra incognita

I don’t mean to brag, but the Diptera families I have found so far this year have been relatively familiar from my preliminary youthful investigations. Some were bonus families due to taxonomic splitting where subfamilies have been promoted to families (Limoniidae, Anthomyiidae), and a few were putting a name to something that I at least knew by sight (Anispodidae, Dryomyzidae, Heleomyzidae, Sciomyzidae), but there weren’t any leaps into the unknown. But now I have taken the plunge.

Small flies are quite off-putting to identify, the taxonomic characters being harder to see, or possibly requiring me to acquire better optics and lighting. But for some reason I decided not to ignore this particular fly sitting on a post with its pals enjoying the first warm day in a week of unseasonably bitter Easterly winds. The warm weather had inspired an excursion to look for dancing moths, my entomological highlight from last year, a by-product of getting away from it all to avoid the omnipresent Royal wedding nonsense.

On top of a hill where the oak canopy happens to be conveniently at eye level, I came across first one and then a hundred delicate moths dancing in the sunshine. Their antennae were several times longer than their bodies and so slender that they bent in even a slight breeze like the bow of a mast in a tempest. Their bodies glistened with a metallic sheen as they settled each on their own oak leaf, near neighbours but not too close, a couple of antennae lengths apart. Then at some invisible sign they would all launch themselves into the air and bob up and down for a bit, glittering in the sunlight. It was a sight I had never seen before, perhaps something no-one had ever seen before, and I felt like an explorer of strange lands. But, of course, these moths (Adela reaumurella) and their dancing are well known. Even so, a year later, the pleasure persists of having chanced upon something so delicately beautiful.

Adela reaumurella Photo Katty Baird

It’s a bit of a stretch to say that the same euphoria applied to finding this microscopic fly, but it’s cut from the same cloth, as was meeting up with the dancing moths again. When I looked at this tiny fly under the microscope, the pattern of veins on its wings was unusual with a knife shape formed by the leading edge (costal vein) and the next vein (R4+5) with all the other veins almost invisible against the transparent membrane of the wing. Something about that pattern was familiar – and sure enough there it was as Figure 58, Scatopsidae, in my Oosterbroek key to Diptera families. There are 46 species in the UK, breeding in various kinds of rotting things with the adults visiting flowers, but I had never seen or heard of them. According to Coyler and Hammond’s Flies of the British Isles, one species (Anapausis soluta) has been recorded swarming in large numbers in the noonday sun on wooden fences and similar places”. There is nothing new under the sun, as it says in another old book.

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