54. Hybotidae – form & function

At last! A fly of character. Although small, it has plenty of style – the thighs on the hind legs worthy of a sprint cyclist, though unlike those of a serious cyclist, they are unshaven and delicately feathered with bristles. The front legs are more delicate, the thorax nicely humped, the abdomen and wings long, the eyes the full height of the head with polkadot reflections (more bulging in life), bead-like antennae with a long terminal arista, long hairy palps sticking out in front and a sharp proboscis below – a fly with panache. But what is it all for?

On my occasional forays into mending things in the house, I am often rewarded when I take the time to look at the engineering of the thing I am trying to repair – why is the piece I am trying to fit back into place that particular shape with a screw hole just there? There is often a good reason, and so it is with flies. Did you guess that a fly with a needle-like proboscis and large eyes might be a predator? Those long palps are in the perfect place to sense when the prey is in the right place for piercing, and the long wings and humped back suggest a strong pursuit flier, capable of outgunning smaller fry. And the monstrous hind legs – could they be used for catching or crushing the prey?

They could, but unfortunately for the neatness of this story, there are plenty of other flies in the family that are also aerial predators but have normal-sized hind femurs. The images I can find of females in the genus suggests that their legs may be more elegant than the puffed up ones of the male. So perhaps hind femur girth is a character that is sexually selected, and the panache of this fly is that of Henry IV of France who wore a white plume in his helmet, the famously extravagant gestures of Cyrano de Bergerac, and the peacock’s tail. Form and function have a more complicated relationship in a fly than in an electric kettle.

53. Chloropidae – special interest

This is another speck of a fly pootered up from the net after sweeping, and what is there to say about it? It’s small and glossy black, and the only interesting thing I can find to say about it is that it has an enlarged ocellar triangle that forms a glossy top to its head. I don’t know which species it is, but whatever it is there are another 177 British species in the family, and I would guess that this is more than twenty times the number of people in the UK that are interested in them, specialists within an already specialist field. Why would they do it? Putting names to things starts in childhood, and there is always pleasure in being able to say what a something is, particularly with obscure beasts like these. Perhaps there is also a comfort in taming some of the uncertainties of the world so that whatever else is going on, at least this one area can be known completely.

Except that this doesn’t work – the collection is never complete. There are new exotic species to add and species to be discovered that have been here all along but overlooked in some previously unexamined locality. Different approaches such as DNA sequencing field observation may reveal the presence of cryptic species hiding amongst what used to be a single species, or may require species to be merged together as being mere variants of a single species. And of course the enthusiast will want to know the distribution of all the species in the family, a daunting task even for an easily recognisable group like Bombylidae (bee flies), but well-nigh impossible for a large family of minuscule flies which only a handful of people can identify. For each species there is also a backstory of adult and larval food sources, behaviour, habitat preferences and climatic requirements, all synchronised to the seasons so that the cycle can continue. At some point the life of the fly will overlap with that of humankind – even these humble chloropids turn out to be significant agricultural pests of rice and wheat in the tropics, where they can also become nuisances about the eyes and nose because of their sheer numbers and by acting as vectors for pathogenic bacteria. So if wrapping everything up nicely isn’t the reward for specialisation, what else can it be?

Yesterday I went looking for hibernating moths in some Berwickshire coastal caves and, having my pooter with me, caught a few flies that were lurking along the dark passageways. They turned out to be a banded-legged Limoniidae, a fungus gnat (Mycetophilidae), several species of Heleomyzidae and a single Sphaeroceridae. What were these flies doing in a cave in the heat of July and which species were they? What harm could come from finding out a little bit more about this nicely defined habitat and fauna? Of course I would need to go back and see what is there at other times of the year, and in other caves, and that’s how the disease starts. Curiosity is the gateway drug of specialisation – you think you can handle it but before you know it, your life will be overtaken by the need to know more, a spiral descending into lonely depths from which there can be no escape. So next time you see a specialist, pity them in their addiction.

52. Ephydridae – pooters

To my shame I find that I have very little to say about this tiny fly. It was part of the catch from a boggy area where there was little else to find. In fact that paucity is probably why I caught it – when you have gone to the trouble of swinging a net about and then sticking your head in to see what’s there, you want something for your efforts. So this ended up in my pooter because there was no competition from larger, more colourful and frankly, more interesting flies.

A pooter is, I have discovered, an essential piece of kit for a dipterist. It consists of a tube that you put in your mouth connected to a tube that you place near your target fly – in between the two tubes is a vial of some sort. When you take a sharp intake of breath the fly is sucked up into the vial and, an important detail, doesn’t end up in your mouth because there is mesh over the end of the tube that you suck. I put my first one together with some fish tank tubing, a plastic cake decorating tub and some electrician’s insulating tape, and was very proud of it. It’s somewhere in the undergrowth on a path down to the sea beside Tantallon Castle. Version two was made along the same lines, but with a smaller collecting vial, and met the same fate on the dipterists field meeting. My third version was therefore going to incorporate all the best ideas I could glean from other models.

I have gone for the “two tubes at one end” version so that the tube can be easily swapped for an empty one without having to pour out flies in the field, and I have used a glass (spice jar) container since plastic is softened and clouded by ethyl acetate (what most people use to kill their catch). I don’t have a one-way valve to stop escapees, preferring the low tech twist of grass or twig method of plugging the open end. The lid has a screw top lid so that it won’t pop off accidentally – there were horror stories of this happening, and of course it’s always the best flies that escape. Since I have now used up the last of the fish tank tubing, I can afford no further mishaps and so I have added a lanyard. Hopefully it will catch some interesting flies ….

51. Agromyzidae – stymied

This is a family I had been keeping up my sleeve for a rainy day, or worse. In December when flies were thin on the ground and I just needed just one more family to reach Dipteran glory, when all the world was doubting me and there was not a fly to be seen, I would put on my coat and hat and scarf and gloves and walk down the lane through the puddles in my wellies and nonchalantly stop at a holly bush, and there I would be sure to find evidence of Phytomyza ilicis, a very common member of this family of leaf-miners.

So I was slightly wrong-footed by this tiny fly turning up as a result of my improved work rate and vigorous sweeping technique. There isn’t a lot to see even at high power, and even though my new microscope is turning up tomorrow (!), I don’t expect to get any further identifying this specimen down to one of the 407 British species – they are more easily identified from the host plant and shape of the mine than they are from the adult fly. There is a very good website devoted to the leaf mines produced in Britain by moths, beetles, wasps or one of eight different families of flies. They don’t even post a picture of the adult insect – it’s all about the mines.

And of course when you starting looking at leaf mines, there is a whole new world of detail to think about – which side of the leaf was the egg laid on, does the mine start near the midrib and does it cross the midrib, is it a wandering line or a blog, what pattern do the droppings make – and many more characteristics too subtle for my eye yet. Having tried quite hard to find micro-moth leaf mines last year, I can confirm that it is hard to walk at a socially-acceptable pace while examining every leaf for signs of damage – maybe I will save a more detailed study of leaf mines for when I am really old! Though planning ahead doesn’t always work out, does it.

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!

49. Ceratopognidae – irritations

Don’t get me started. Where are the little blighters when you need them, and where did the one I eventually caught get to? Although I have no proof, anyone who has visited Scotland in the summer will not doubt me when I claim that I have seen that diminutive, unsettling presence of still summer evenings, the biting midge, a member of the family Ceratopogonidae, one of 40 British species in the genus Culicoides.

from British blood-sucking flies, F.W. Edwards, H. Oldroyd and J. Smart (1939)

Irritations are always more severe when they have been going on unnoticed for a while – the hum of distant traffic, the strobe flicker of light through trees from a low sun, the shirt label scratching at your neck. Eventually the dripping tap of annoyance slips into consciousness and by then it is too late – the mental tools that might have let you keep your cool are overwhelmed and you flail about ranting at whomever or whatever it was.

Now the reaction I get when I tell people that I am interested in flies is not always positive. There is “Yuk!” and similar one-word responses – clearly from people who haven’t been following my blog. There is the more engaged “Oh I saw one the other day, ….” where they proceed to show you a fuzzy picture on their mobile device of something that clearly is not a fly, although sometimes it may have fly as part of its name. There’s the squeamish “How could you kill them and stick them on a pin?” followed by a lecture on the sanctity of life before they slap the midge on their wrist and drive off in their insect-bespattered vehicle to eat their insecticide-dependent dinner. And there’s the look of incredulity and startled suspicion from people who conclude that they must be in the presence of a monomaniac with a dangerous disposition. This might be the time to turn to British-blood sucking flies which quotes a W. Derham, Rector of Upminster in Essex, in his description from Physico-Theology: or a demonstration of the being and attributes of God from His Works of Creation (1713) of what were then called “Nidiots” as being “greedy blood-suckers, and very troublesome where numerous” – referring to members of the genus Culicoides of course – what did you think I meant?

In the same way, I also have some way to go before being able to think of midges as anything more than irritants, the very reason that a book has been written about them – Midges in Scotland by George Hendry – an honour not many genera of flies can boast of. The chapter on Culicoides in British-blood sucking flies says: “Wherever it occurs, Culicoides impunctatus is an exceedingly troublesome insect, and in the western highlands of Scotland is a major pest, sometimes rendering outdoor activities impossible.”. Yet, the frontispiece of the book is a drawing of the pest, patiently rendered down to each tiny spot and microscopic bristle. For the enthusiast, there is also an Appendix describing, with illustrations, “The genitalia of the British culicoides with notes on synonymy.” I have no idea how you to dissect out the genitalia from flies that are already too small for me to find again after putting one in a tube. But just the sight of their tiny bits and pieces was beginning to make me irritable at the thought that, had I not lost the fly, I would have had this impossible task ahead of me in order to identify it with certainty to a species. But then I remembered that the males don’t bite and so this definitely biting midge would have been a female. I can, for the time being, remain serene.

48. Tabanidae – dilemma

So far I have been a virtuous dipterist, only counting fly families that I have caught myself. But spending a week in the company of experts was bound to bring problems, problems that I brought on myself by telling everyone on the first evening that I was on a family quest. So it wasn’t long before, like a lady empid, I was being presented with fly-gifts by eminent dipterists to tempt me from the path of righteousness. Easy enough when it was things like enormously-antennaed sciomyzids, a stylish scathophagid, a colourful dolichopid – these were mere boxes of chocolates and flowers that I could gratefully accept without compromising my integrity since they were from families I had already caught.

Sciomyzidae – Sepedon sphegea
Scathophagidae – Pogonota barbata
Dolichopodidae – Argyra leucocephala

But what of this – the most impressive fly that I have yet had the pleasure of meeting – caught twenty yards from where I was standing by someone putting more effort into their sweeping than I was. It’s a (much) bigger version of the more familiar cleg whose silent approach and stealthy bite I have often suffered from in the past. I wanted it, I needed the family (Tabanidae) for my Year of the fly mission, surely counting it wouldn’t be right. In my confusion I submitted to the humiliation of what I was informed was the traditional fly-on-the-face selfie. After narrowly avoiding crawling up my nose it dropped off, hovered for a moment to warm up its wings, and then took of like a torpedo, saving me from having to decide about whether to keep it or not.

For a day or two I wrestled with the issue of whether or not I could add Tabanidae to my list, my conscience fighting desire in a finely balanced contest until, happily (!), a cleg found me out and sucked my blood until I got a tube over it. Not quite as large a beast as T. sudeticus but the eyes are dazzling, as is the glossy frons between the eyes and the purposeful mouthparts. Note also the quality of the image obtained on a modern microscope – dilemma? What dilemma.

47. Clusiidae – personality

It’s hard to explain why you warm to some people rather than others – or why sometimes you get it wrong and find that your reserve was misplaced. Perhaps their bluster gave you the idea that they were just putting on an act, or their shyness meant that there was nothing interesting about them, but you were wrong. And, conversely, after a while the “life and soul of the party” type might get on your nerves, the raconteur become lost in telling their story, the empathetic soul mate overwhelming in their intensity.

And so it is with flies. What dipterist hasn’t had their head turned by the flashy hoverflies, been dazzled by the symphony in bristles offered up by the calypterates (Muscidae, Fanniidae, Anthomyiidae, Calliphoridae, Tachinidae, Sarcophagidae, Scathophagidae, Rhinophoridae), or tried to make friends with the gangly-legged craneflies (Tipulidae, Limoniidae etc.) with their antiquated articulated antennae and dour expressions. So after being scared of acalypterate flies as being too small, dull and indistinguishable, I now find myself drawn to this kind of bashful pallid fly. Who could not find this fly beautiful!

It almost looks as clearly laid out as the diagrams in the front of the identification keys – black bristles and clear wing veins against a blank background. All its features are presented without fuss, no need to adjust the lighting to see a stumpy black bristle hiding against the reflections of a glossy black thorax, no missing those bold bristles on the head. It is an open book – to the extent that I can almost see through it. It was even a pleasure to identify – the second segment of the antennae having a strange shape that was familiar from a couplet I had often passed through but never been detained at – “Second antennal segment triangular at outer side.” So it was and everything else fitted too. Using Alan Stubbs’ key to the family from 1982 got me to the genus Clusia, it being entirely yellow, and of the two British species, this one fits flava since the other one – tigrina – has very spotty wings and currently only with records south of Leeds.

I am smitten. What was this fly up to when our paths happened to cross? Where had it been hiding? Where did it spend its early days? How can we meet again? Colyer and Hammond in Flies of the British Isles boast of taking four species in the family “by sweeping over a wet, disintegrating beech stump in the New Forest”. I think they were keen on them too.

46. Pedicidae – optical envy

As a result of trying out the experts’ industrial-scale collecting technique, that evening I had a full tube of tangled flies to sort through – first of all to pin and then to work out which family they were. Though it wasn’t alwasy necessary, I went through the family key for everything, finding flies in the familiar families of Syrphidae, Keroplatidae, Drymoyzidae, Fanniidae, Mycetophilidae, Scathophagidae, Sciaridae, Opomyzidae, Limoniidae, Dolichopodidae and Lauxanidae. With each journey through the key I became a little more casual, skipping the first 80 couplets when it was obviously an acalypterate. I didn’t even look at the key for the cranefly family Limoniidae, knowing that I had to check that there were two anal veins in the wing, that there were no ocelli, that the eye was bare, that the last segment of the palps was short and that the vein before the anal veins didn’t have a sudden bend in it.

Just as well I was checking, for this fly looked, to me at least, just like a standard Limoniidae – i.e. a small drab cranefly with unmarked wings that I would probably struggle to get to genus and species with. But checking its eyes there was no mistaking the presence of tiny hairs between the facets – giving a silvery halo to the head. At least, that’s how it looked using the binocular microscopes provided for us to use for the Dipterist Forum field trip week – the photos above at low, medium and high magnification show that it’s a bit more of a struggle to see those hairs now I am back home using my own instrument.

This microscope was a present from my Great Aunt, Dorothy Knull who studied Hemiptera, particularly the brightly coloured Cicadellidae or leafhoppers – my microscope is the one in front of her in the photograph, and my computer now sits on that same desk. Her husband Josef Knull was also an entomologist focusing on beetles, and they worked together at Ohio State University from 1934 for the rest of the working lives and on into retirement. Meeting them in Columbus in my early teens was what started me off on insects in the first place. The make of the microscope is Spencer and the serial number 289290 which dates it to 1948. I suppose the optics could now do with a clean – on the highest power the image is especially murky and dusty. My light source is an Ikea reading lamp re-purposed from my eldest son’s bedroom, and could probably be improved upon, although I have to say it is much better than any set up that I have had previously.

Although it feels like an insult to her kindness all those years ago, having now spent a week with a modern instrument in which you can increase the magnification smoothly rather than in big jumps so whatever the size of the fly you can make it fill the screen, its colours brighter, the focus crisper and the lighting more intense, the scales have fallen from my eyes – I had imagined that a new microscope would cost thousands of pounds – but is seems that that is not the case, and it would be nice to see those eye hairs clearly.

45. Lonchaeidae – habits

My first trip out fly collecting with the Dipterist Forum experts started badly. We set off at an amble down a woodland track after having admired each other’s pooters, and I began looking for likely-looking flies. My normal technique is to spot a fly, get up close enough to see if it is worth catching, retreat to make room to swing the net, and the fly usually takes off just as I get into range with my short-sighted eyes. In contrast, the experts set off thrashing their way through the herbage with their wide-mouthed nets. With a side to side flick they kept the catch caught, and after a few minutes stuck their head right into the net to inspect the harvest and suck up a representative selection. After ten minutes they all had pooters bubbling over with interesting stuff and I had nothing.

We came to a bridge where an elder bush leaned over the parapet in full sunlight. Peering over to the stream below, I was gently moved aside by one of my companions in order to make room for a purposeful swipe of his net at the elder leaves just at my elbow. “Ha! Lonchaeidae – very nice.” Not only was my spot and catch technique less effective than their sweeping, but I hadn’t even managed to spot this desirable fly, a fly from a family that I had never seen before.

So I switched to their method and took off grumpily into the woods, sweeping relentlessly over mossy banks and puddles, rotting stumps and nettle patches. My technique needed a bit of honing, first to take my glasses off and get my head into the net, the net held pointing up towards the sun so that the flies would crawl or fly upwards away from head. Then, while still holding the net just so I had to get the right end of the pooter into my mouth and the pooter into the net and with my third hand maneuver the tip so as to suck up a chosen fly. There were many tantalising escapees, and I eventually reverted back to my old fly hunting method, turning up the cranefly Tipula maxima, the largest British fly by wing span, though possibly not by weight.

When I got back to the bridge it was still in sunlight, and waiting for the others to reappear and wondering if flies were also creatures of habit, I stood guard at the elder bush waiting for action. Sure enough, a few minutes later a hump-backed, black-bottomed fly arrived to sun itself on the very same leaf that the previous trophy fly had been taken from. I swiped and missed it, but back it came again and this time I got it, potted it and here it is, a very nice fly indeed.