44. Diastatidae – known unknown

It is a continual surprise to find that whatever I scoop up in my net, someone busybody has been there before me, describing what I’ve found, fitting it into taxonomy, documenting its habits and distribution. Even those specks that look like they could squeeze through the mesh of the net or might be missed when emptying out a pooter have all already been described. On the one hand it’s comforting to know that even this small-scale territory is known, and their diminutive features known. But it’s also somehow disturbing to think that it has all been done, that new discoveries aren’t waiting for me when I walk out the back door.

This is quite a natty fly, with its unnecessarily long head bristles that point every which way, a tousle-headed rascal. The antennae are delicately plumose (feathered) and there is a nice balance of grey for the body, yellow for the legs and face and a classy red for the eyes. Also rather pleasing are the graded bristles along the front edge of the wing, ending with a big spike before the subcostal break. Six species in the family are found in the UK, and according to Peter Chandler’s 1985 key only one (Diastata fuscula) has wings that are unmarked apart from a blush of brown above the subcosta, just beneath that fine row of bristles.

When I arrived at Stirling for the Dipterists Forum field meeting, a couple of enthusiasts were already heading out to see what they could find in a patch of wet woodland they had spotted at the University entrance. I rushed to unpack my collecting gear and follow them and found some woods, but though I scoured the slopes and diligently swept my net over flowers, foliage, rotting tree trunks and mud there was no sign of the others. At least I found this fly, which according to the NBN map is only the fifth Scottish record south of Perth. And when I gave up on the woods I did find a legendary dipterist working the muddy edge of the campus pond and so I tagged along to learn how it should be done properly. All nice and tidy. Except that it turns out that the larvae of this family are unknown – there are yet some chinks in the armour of knowledge. I’m off to check my local woods for flies and glory!

43. Anthomyzidae – small fry

This may be one of those dreaded fly families about which there really is nothing much to say. Flies of the British Isles has a single page on the family, half of which is the description of its bristles and wing veins. The larvae develop on the leaf sheaths of grasses and rushes but don’t seem to be agriculturally problematic.

This fly was just a speck pootered up from the net in desperation, all the larger flies having being discarded as uninteresting members of previously found families. There’s not much to see – even less now that the tiny head has somehow pinged off – the pin it is on is so flimsy that it bent trying to push it through a paper label. The thorax and abdomen are black and undistinguished, the remaining legs are yellow and the wing has what I am coming to think of as the bog-standard acalypterate pattern – three longitudinal veins, a couple of cross veins, and a couple of smaller veins that don’t quite reach the wing margin. Yet under high magnification, perhaps even this minnow has some charm. The leading edge of the wing is fringed with evenly spaced tiny hairs.

Close inspection of the front legs reveals a stylish line of long hairs upon the underside of the femora, and sticking out like a sore thumb, one quirky, thicker bristle, a characteristic of most of the genera in the family. And now I think of it, the yellow legs contrast rather nicely with the rest of the fly. If only the head had stayed on then I might have found some even more endearing features, and I might have been able to put a name to the face.

42. Opomyzidae – therapy

It has probably been obvious as the Year of the Fly has progressed, that I would soon be needing professional help. At first I pretended that there was nothing wrong with spending long hours immersed in the study of trivial minutiae, with obsessive poring over arcane, out-of-print texts. There were unexplained parcels surreptitiously stowed away in my private den and late nights of taxonomic frustration before restless sleep and an early rising to continue the self-imposed flagellation. Eventually I could see that the trend was towards an unhealthy set of solitary, even anti-social behaviours, with daily communication with non-initiates becoming increasingly awkward, even incomprehensible.

Eventually, I booked myself onto a week-long retreat where I would have the chance to meet some fellow-suffers and, with their support, begin the healing process. I was nervous at first, not knowing most of the other attendees, except by repute, and I worried about what form the treatment might take and how distressing it might be. It was probably against the rules, but once I had unpacked my things I couldn’t resist a quick pre-dinner wander with my net up into the wooded hills that loomed over our isolation wing. A few last flies couldn’t hurt. Amongst the illicit treasures were some tiny, unfamiliar acalypterates with spotted wings, no vibrissae, no preapical dorsals on the mid-tibiae, a complete subcosta without a right angled bend – Opomyzidae. Really it was shame to be giving up this altogether innocent pastime when it was becoming so easy.

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At our first communal meal there was the usual awkwardness of finding out everyone’s name and teasing out the particular nature of their affliction. Each heart-breaking story seemed to begin with a childhood enthusiasm gone wrong, though for some there was a long relapse with the symptoms not surfacing again properly until retirement. Whatever the trajectory, the disease had now overwhelmed all resistance and brought each participant to their present crisis.

Or so I thought. After dinner the group hurried off to a laboratory generously supplied with microscopes and unashamedly succumbed to their weakness, exchanging specimens and exclaiming over particular beauties, Latin names crowding out English words. Instead of self-reflection, small-group workshops and the sharing of experiences, the evening degenerated into excited and shameless planning of how they could indulge in their obsession for the rest of the week. Some of them, it transpired, had been attending this same kind of retreat every year for decades now, and instead of hoping to effect a cure, were joyously resigned to their fate. I may have misunderstood the purpose of the Dipterists Forum.

41. Stratiomyidae – walking

I am beginning to realise that a fly collecting walk is not like an ordinary walk. As a father’s day treat I was allowed to plan an excursion between breakfast (cooked by one son) and lunch (cooked by my other son). I spotted a reservoir on the map that I hadn’t been to before and so off we set, down the side of a field where pugilistic hares tore back and forwards in the distance, and then down through a plantation to the shimmering water’s edge. Already I was falling behind as I idly swept the grass verges and woodland ferns, periodically inspecting the harvest. There were empids playing along the surface of a lade and furtive tipulids making merry in the long grass. A pile of swan manure was worth a look, and also a well-plucked pigeon carcass, and eventually, without having found anything worth putting in a pot, I caught up with the rest of the party at the bench where they were waiting, almost patiently.

Now the sun was out and there were flies playing in every shaft of sunlight and swooping by, flies in swarms overhead and no end of flies of interest posing on well-placed leaves. Each flower had its customer, each puddle a gaggle of minuscule sea-gazers and the undergrowth was thick with fly flittings. It seemed that the slower I went, the more I saw, and that the best strategy might be to find a good spot and just stay there. And in one such, busy, sheltered, sunny spot I found this jewel of a fly, a tiny green hoverfly at first glance, but I suspected it was not.

Under magnification the antennae have more than three segments, though they are well disguised, and the wing has a peculiar arrangement where lots of veins are crowded into the leading edge with a tiny pearl in the centre of the wing, the discal cell. These are the features of soldier flies, so-called because of their striking colours and marking – presumably meaning soldiers of a previous era, as modern-day soldier flies would be much better camouflaged. For identification purposes the bible is “British soldierflies and their allies” by Stubbs and Drake, which I have yet to acquire, so I made do with my photocopied Royal Entomological Society key by Oldroyd (1969) which brought me to Microchrysa cyaneiventris or Black gem. The excellent Provisional atlas of soldierflies doesn’t show any previous records for East Lothian, though the species is widespread in the UK.

I did eventually emerge from my fly walk stupor, striding out and looking straight ahead so as not to be distracted by this and that, and so caught up with the rest of the family to a gentle ribbing. Of course, there was a time when the slow boot was on the other foot, and every puddle had an attraction for the boys. Stones had to be carefully selected and dropped in, flowers had to be plucked and scattered, so that walks were a meandering trail of detailed destruction. There were also crawling things to be pursued and butterflies to be chased and lost. And though they would strenuously deny it now, there was even time to greet each fascinating fly. To quote Calvin and Hobbes, “There’s treasure everywhere!”.

40. Sciaridae – see and believe

Whenever you use keys to identify things, there are always a few couplets that have intriguing descriptions of some feature, but which, sadly, don’t apply to the thing you are looking at. It’s the same flicking through pictorial guide books where your eye is arrested by some glorious creature, surely too fantastic to occur in Scotland. Every time you go through the book checking the identification of something mundane, there it is taunting you with its attainability. Then, some lucky day, there is the mystical creature before you, those impossible characters brought together, like when both lenses of a binocular microscope snap into place and you can suddenly see clearly.

I have had this experience most often with moths – first with the Old lady, a fairly drab, brownish moth but twice the size of everything else on the page, and which turned up, larger than life, excitingly in a moth trap and then even more thrillingly, on alders by the river that I had especially baited with treacle with the very hope that she might turn up. Even more recently, the astonishingly marked Peach blossom moth appeared in a fly trap that had been baited several weeks previously with black pudding. Nothing seemed interested in it and I forgot all about it until one day, making another delivery to the compost heap, I glancingly noticed that along with some slugs and fly pupae and the revolting, semi-liquid remains of the bait there was this most beautiful of moths, its blushing peach blotches as fey as a summer frock. There are many more such matches still to be consummated, like the Scottish primrose which one day I will find when lounging on the sward of a northern sea cliff.

In the fly family key, there are couplets that I hardly read any more since my specimens obviously don’t have a complex grid of secondary veins on the wings (Blephariceridae), eyes on stalks (Diopsidae), a bloated abdomen (Acroceridae), a head entirely covered by the eyes (Pipunculidae) or ridiculously fat back feet (Platypezidae). A less extreme couplet that I had noted, but never had reason to pause at previously, mentioned an eye bridge above the antennae. Suddenly this made sense as I got the high magnification on a tiny dark fly from the bottom of that morning’s moth trap (the highlights being a Poplar hawkmoth, a Buff tip and a Small clouded brindle). I had thought that this speck of a fly might be a fungus gnat (Mycetophilidae), but the monobrow eyes and the tuning fork like M veins at the wing tip place it instead in Sciaridae, formerly a subfamily of the fungus gnats. Unfortunately, my photographic set up is not good enough to capture the eye bridge and so it will have to remain something that you see for yourself. For the same reason I can’t share another remarkable sight of that magical dawn, a unicorn grazing in the meadow.

39. Psilidae – character

Have you ever seen such a boring fly? It’s a pallid colour with see-through legs, hardly a bristle on it apart from the remnants of a bad hair cut on the back of the head, and an undistinguished pattern of veins on a not-quite clear wing. There are no unusual thickenings of the legs or distortions of the thorax, the antennae are just the normal three segments with a slightly feathery arista (the thin hair that sprouts from the base of the third antennal segment) and the abdomen is just a uniform blob of bland yellow brown. Even the common name of the family – rust flies – derives from the rusting produced by the larvae of Psila rosae, the carrot fly, on carrots, rather than from anything interesting about the flies themselves.

Yet it turns out, that in the same way that people are always more interesting than mutual reticence might at first suggest – like the stranger you get talking to at the bus stop (now my dream analyst, squash pupil, bicycle mechanic and cake-sharing buddie), the viola player in your amateur orchestra (despite all the viola jokes, now my wife), or the furtive net-swisher in the woods (actually, its probably best to keep well away from them), even this fly has character when you spend a little time getting to know it better.

For a start, the head is an unusual shape, receding severely from the a pointed front, the antennae slung below, and no hint of an upper lip or moustache. Another peculiarity is that about a third of the way along the front of the wing there is a faint vertical line where the membrane is clearer than elsewhere, and this clear line wanders down the wing, slanted back towards the body, like a tiny snail trail. That subtle feature and the absence of bristles in several crucial places are the characters that place this fly in the family Psilidae.

Following the key by Darwyn Sumner, and eventually realising that I had put the pin through the exact spot on the thorax where a crucial bristle should have been (visible however, on the other side) brought me to the conclusion that this was Psila fimetaria, a widespread species of low plants in damp places, which is indeed where it was found. The final couplet asked if the antennae has a dark patch where the arista emerges from the antennae, and when you get up close, it turns out that it does. Had we not got to know each other so well, I would never have noticed that affecting detail. None of us are entirely boring.

38. Asilidae – joy

There are a lot of flies in the world – about 17 million for each of us according to Erica McAlister’s quirky book The Secret Life of Flies. But I think it is safe to say that most of us don’t pay our quota of flies much attention, and when we do our feelings are mostly irritation, disgust or indifference. How different a world it could be.

Yesterday, I had the afternoon off at a work-related retreat / conference / jolly and instead of going clay-pigeon shooting or mountain biking, elected for a fly-catching meander along the banks of the Tay along with a select group of fly-curious colleagues. Because of the river there were stoneflies and mayflies but we held steady to our task and refused to be too excited by moths (last year’s target), beetles (too hard), bugs (also too hard) and spiders (next year’s target). Some ineffectual net waving was eventually replaced by more directed and vigorous sweeping of the sward, and the flies began to appear – a moth fly near the hotel drains, some empids with big front feet, some fat muscids and small dark anthomyiids, a cluster of drosopholids on a moist bracket fungus, some “interesting” acalypterates retained for further questioning, and then the star of the show, the talking point of fly-fanciers late into the night, the unexpected bounty of a monstrous, stylish, finger-friendly robber fly.

It has been a long time since I have seen one of these, but I was hoping one would turn up for the list of course, but also just for the pleasure of seeing one. The adults are predators, largely of hymenoptera, so that the alternative name of assassin flies seems more appropriate as they lurk about waiting for unfortunate passers by to pounce upon and suck dry. At any rate I was keen to get this magnificent beast into one of my collecting tubes so that I could inspect its distinctive features (saddle-shaped depression between the eyes, bristly mystax (beard), piercing mouthparts, mouth-wateringly complex venation) at my leisure. However, the fly-fans pounced on my entomological heartlessness and made touching pleas to spare the life of this fantastic beast. “You’re not going to stick it on a pin, are you?” So, not being a beast myself, I relented and, with much rejoicing, it was released to fly free. Oh that each of our allotted flies could bring us this much joy!

37. Sarcophagidae – hard graft

Empididae
Tephritidae
Syrphidae
Piophilidae

New families are now getting harder to find – I had high hopes from a batch caught during a work day lunchtime break with a fellow dipterist. He pointed out a mob of flies purposefully cruising back and forward over a stream, just out of net reach until the wind eddied slightly and brought them within striking distance. They sported unusually inflated front feet, but turned out to be Hilara, a genus of Empididae. Also promising was a fly with jauntily spotted wings swept from the edge of a bean field, but this was Trypeta zoe, a differently patterned Tephritid. Next, a greenish metallic fly swept from a buttercup-filled meadow was at first sight a hover fly, but seemed to lack the distinctive spurious vein of the Syrphidae. But all the other routes through the key ended up at families that were plainly wrong, and so eventually I concluded that it was Lejogaster metallina, a hover fly that can be confused with a soldier fly (Stratiomyidae); unfortunately for me this was the hover fly. My last hopes were pinned on a tiny fly also swept from the meadow that I thought might have been Drosophilidae, but my companion knew better, being an expert on the family. Of course he was right, and it turned out to be another Piophilidae.

Finding new families was becoming hard work, so it was somewhat of a relief when, as I was enjoying my breakfast outside, my toes dipped in clover, a distinctively purposeful and noisy fly joined me in the sunshine. As I got up to fetch my net it flitted away, but since we had both identified the sunniest and most sheltered spot in the garden, I suspected it might be back. With the net by my side I continued to contemplate the possibilities of the day. Half a cup of coffee later it landed on my net and with an expert flick of the wrist I curtailed its morning salutations. This was, without my needing to go through the key, a flesh fly of the family Sarcophagidae, as smartly turned out as a chap heading out to work in suit and tie. Its thorax was a neat pinstripe of grey and black stripes, set off nicely by gold dusting between the eyes, the abdomen tesselated in glinting black and grey, an eye-catching tweed.

I assumed that being such a large beast, taking the identification further would be trivial, possibly not even needing the microscope. I started off using my photocopied key (1954) to Calliphoridae by van Emden which includes what was then the subfamily Sarcophaginae. Finding the genus was a struggle through couplets asking if the hind coxae was setulose, about a row of inclinate frontal setae, and if the mid tibia had a postmedian ventral seta, but I cautiously arrived at Sarcophaga, for which the key noted: “The chaetotaxctic characters [ie. the bristles] are somewhat unreliable and the only way of obtaining quite definite identifications is by comparing the male genitalia.” With an updated version of the genus key I stumbled along, confirming that vein R1 was not setulose, that there were four presutural dorsocentrals, that abdominal tergite 3 had strong marginals – which brought me, possibly, to a choice of three widespread species, S. subvicina which is a parasite of earthworms, or one of a seemingly indistinguishable pair – S. carnaria and S. variegata – for which the first of which the van Emden key notes: “Larvae in decomposing organic matter, including dead animals, sometimes parasitic, even in man, causing intestinal myiasis etc.” The “etc.” was slightly worrying, as was the thought that worm or man, quick or dead, there was flesh fly for whom you were the right kind of food.

36. Mycetophilidae – cheat

Another wet weather find from the woods, a tiny but distinctive fly with long, out-of-proportion legs peppered with needlessly vicious bristles and spurs, and joined to the thorax with what look like grains of rice. In comparison the thorax was tiny and so hump-backed that the head was tucked underneath it. I knew what this was, but, with an eye to propriety, I put it through the family key anyway. Does the fly have wings? – Yes; long antennae? – Yes; two anal veins on the wing and a V-shaped suture on the thorax? – No to both of those; ocelli present? These are the three (or sometimes two) primitive eyes that sit on the forehead (frons) between the larger compound eyes and they were missing. It keyed out as Ceratopogonidae, a biting midge.

Except that, that it wasn’t – it’s a fungus gnat, Mycetophilidae. Working backwards through the key to see where I might have gone wrong, it turns out that there should have been ocelli. Even on a small fly these are usually easy enough to spot since they are slightly raised up from the level of the frons on a beady-eyed triangle, often with bristles at either side. The frons was textured with little bumps, but try as I might I couldn’t convert any of them into ocelli, even on the highest magnification and with the lighting optimally adjusted.

Perhaps I was wrong about this being a fungus gnat, but the venation shown for Ceratopogonidae was all wrong, and apart from the missing ocelli, the fly had all the features expected for Mycetophilidae including the venation of the wings which is described as “characteristic (vein CuA1 and stem of veins M1 and M2 not connected or connected as far up as crossvein H).” A Royal Entomological Society key to the family from 1980 by Hutson, Ackland and Kidd says that the ocelli are sometimes in a row rather than a triangle, or can be reduced to two, either right on the midline of the head or on the very margin of the compound eyes. And indeed, I could almost persuade myself that in certain lights and angles there were glimpses of two tiny pustules at the highest and broadest point between the eyes – at least that’s how it seemed when I looked at it with my third, blind eye.

35. Lauxaniidae – bristles

4th June 2019

Even though it was rainy, the cat and I went for a walk in the woods, both being tired of indoors. The cat sniffed and listened, tail and whiskers alert for interest and danger, yet indifferent to the nearby bark of a deer, frighteningly close if it had been a dog. Because of the rain there were a lot of refugees using leaves as parasols and I moved along at cat speed, looking upwards through the canopy for tell-tale shadows, turning over soft green new leaves where aphids hunched, spiders crouched and flies took their ease. Some inept tube-work lost me a few interesting-looking ones, and eventually, our paws and beard becoming damp, we headed home. I resorted to sweeping the undergrowth, careful for the snag of bramble tendrils, and this one caught my eye in the net because of its buttery colour, nothing quite like anything I have caught so far.

Bristles are often important in fly identification, and on a dark fly they can be a bit of a pain, the lighting having to be just right and the fly at the right angle before you can see them. No such trouble with one. There are no bristles (vibrissae) at the mouth edge beneath the eye, but there is a bristle at the end of the tibia of the middle leg on the top side (and underneath as it happens). The anal vein, which is the one nearest the bottom of the wing, is short and doesn’t reach the wing margin – the vein above it also doesn’t quite reach the margin, but peters out just after the cross vein. Finally, the P bristles are converging, forming an X shape behind the ocelli which are three primitive eyes that sit in a triangle in the centre of the forehead between the large compound eyes. These characteristics place this mellow fly in the family Lauxaniidae, while a key to the genera, also depending heavily on bristles, places it in the genus Meiosimyza.

Dipterists have an almost comical interest in the position, size and orientation of the bristles on their subjects. But apart from taxonomic utility, the precision with which hairs, bristles and spurs are placed upon the body provides one of the delights of looking at flies under a microscope. There are graded girths and lengths of hairs in rows down the thorax, single bristles in particular places, a tuft somewhere else, fancy combs of stubby hairs on the legs, well-maintained mustaches or proto-punk anarchy of hairs that arch inwards or outwards, upwards or downwards, forwards or backwards, pairs that cross or are parallel or divergent. Antennae can have a stubble or exuberant whorls of delicate verticils. The same fly can have no-nonsense jet black bristles in one place and a profusion of soft blonde fuzz elsewhere. The coiffure of flies is a wonder to behold – which is more than could be said for either the cat or I after our walk. But at least we got rid of the cobwebs.