Different Gnats

Gnats. What can you say about them? When I was a young boy, long before I started showing any real interest in diptera, I knew gnats to be tiny, leggy flies that formed small clouds which danced up and down in seemingly random patterns. Up close they appeared skinny and fragile and, if I'm being honest, to my young eyes they looked pathetically puny and unimpressive. 

Fast forward maybe twenty five years to when I'm in my mid-thirties and I'm starting to show more of an interest in flies, admittedly mostly hoverflies, but also a few other 'big and bright' ones. I still watched gnats doing their up and down dancing cloud thing, which by now I knew was some sort of a mating ritual, but that was pretty much all I did know about them. I also knew that without a shadow of a doubt I would never, ever become interested in them.

Fast forward to tonight. I hurried my way through the darkness and light rain, dashed across the grounds and into the laundry shed to inspect the walls and ceiling for signs of beetles and flies. Guess what - two gnats!! No longer the puny and unimpressive things that I had grown up alongside, these were exciting, wondrous beasts to be captured, photographed and marvelled over in my quest to find out what they were and then to share them with you.

This is the first gnat

Well that certainly looks very familiar...

Yep, it was another Mycetophila, one of the fungus gnats that I captured just a couple of days ago. I still haven't tracked down a key that will enable me to figure them to species, so it goes into the box with the other one and will stay there until I have that key. Either that or, as Tony suggested, wave it in front of Peter Chandler who will name it within 1.2 seconds... 

Note the single ocelli reflecting the camera flash.  And WHY are the palps so ridiculously long???

Gnat number two was very different, though.

That's a racy-looking beast, far more streamlined than the bulky fungus gnat!

I thought I knew what it was, but keyed it through by checking the wing venation. I was quickly led to the family Anisopodidae, a small group of flies with only four species known from Britain. Even better, there are keys available for them too! 

Mike Hackston to the rescue once more with this wonderful key. Wonderful except that I still managed to convince myself it was something else! 

There are only three flies in Britain with that wing venation - and I still muddled it up!

Helpfully, this gnat is a male which means I can have a look at its 'tackle', the shape of which differs between the species. Here is a ridiculously enlarged image of just that

You've heard the phrase "tight as a gnat's arse"...

What you're looking at is a gnat's arse. Literally. The shiny black bits are the male's claspers; these clamp around part of the female's abdomen during coupling, ensuring that everything goes according to plan and they don't accidentally separate before mating is successful. Essentially, his and her genitalia fit together like a lock and key and only the right shaped key will fit into the right shaped lock. It's what stops 'wrong' species of gnats mating with each other. Wing patterning and body colouring may vary in a species, but the shape of the male's genitalia doesn't, at least not by very much. Hence it's usually a very reliable way of telling similar looking species apart from each other. 

And this is what it looks like when a professional does it

For some reason, I was convinced that I could see a tiny 'tooth' at the base of each clasper. But only when viewed from the side. I don't know what it was I could see, but something sticks out like a tooth. So I thought I was looking at Sylvicola fenestralis, (number 24 in the image above) which is a common enough species across much of Britain, though not one I'd seen before. 

But the shape and length of the claspers just didn't look right for fenestralis. And actually, viewed face on as in this image, there was no sign of the 'tooth' I'd seen in side angle. In the end, despite there being lots of black across the 9th sternite (a pro-fenestralis feature) it was the width and depth of its notch that convinced me I'd erred. My gnat was Sylvicola cinctus, (number 22 above) which is one I've seen here before. From inside the very same laundry shed, in fact! 

The good news is that there are lots and lots of gnats out there, from many different families, so I get to play with them all over again.