Gnat Dissection

Miracle of miracles, today Skye was spared sideways lashing rain, hail and gales. It was still a bit blowy, but totally bearable outdoors in just a hoodie. I had high hopes of finding flies attracted to the security lights once darkness fell (about 4pm today...it's still very gloomy and cloudy) and sure enough a quick peek at the nearest light revealed several small flies/gnats lifting at my approach. Undeterred, I filled eight pots with a small fly in each - an absolute bonanza!  

Awaiting the ethyl acetate treatment

My method of dispatching flies is quite simple. I add a small wad of tissue paper into the top of the tube, pipette a few drops of ethyl acetate onto the tissue, replace the lid and wait ten minutes. Job done.

Simple and efficient

Previously, I've had a dedicated killing jar (I use an old jam jar) into which I've tipped the captive flies. The obvious problem being that sometimes they fly up and away in a bid for freedom, often straight out the window never to be seen again. My current technique is heavier on ethyl acetate usage but I suffer far fewer escapees. I suppose I could chill them in the fridge and then tip them into a killing jar, that might be even better. I'm not a fan of killing insects by freezing, I've heard that various internal organs may distort, and the genitalia are often critical for a positive ID. Wouldn't want them to swell/twist/split on me.

Of tonight's eight flies, two are Moth Flies (Psychodidae) and there were plenty of those running around the whitewashed wall below the security light. I do actually have a key to these but you need to clear and dissect the body and mount it on a slide. I may have a go (in fact I'm sure I will) but not tonight. For now they are simply labelled "Psychodidae (100spp)" awaiting another day. Crazy mad antennae on them though.

I have a handful that I'll look at tomorrow and there are three Trichocera, the Winter Gnats. I've sussed these now, the gangly legs holding the body poised as if ready to flee (which they often do) and the short, downcurved anal vein that reaches the wing margin make for an easy recognition of the genus. Males have obvious claspers and the females a horny ovipositor, both of which are of a size and shape unique to the various species. Add in wing clouds and lengths of various veins in the wings and an identification should be relatively straightforward. 

First up I checked a male. No wing cloud over r-m, so it's not Trichocera regelationis, the only one of the genus I've seen before (ticked earlier this week, in fact). It keyed through without any problems to Trichocera major, the largest British member of the genus. Here's a pic of its claspers

The long sinuous styles are classic male Trichocera major

Next up I looked at a female Trichocera. No wing cloud over r-m, big old ovipositor, looks good for Trichocera major too. Sweet. Here's a pic of the long ovipositor

I whacked the pics on the UK Diptera FB group for confirmation and pretty soon Julian Small, the resident Nematocera expert of the group, came back with the male is T.major but the female isn't!!! Oh, ok. I keyed it again, paying close attention to everything before leaping off to another couplet, this time it led elsewhere. Oops. I now made it saltator. Julian had obviously come to the same conclusion, for when I checked FB next he'd responded with

Maybe it's just an individual variation, or maybe it's saltator. I reckon there's a good chance of unrecorded species in the more wild and woolly parts of the country. Do you fancy dissecting out the genital plate?

Did I fancy tearing the arse out of a gnat, my first ever fly dissection? Well of course, whatever else would I be doing on a Thursday evening. Seemingly all I had to do was tease apart the last abdominal sternite and tergite and the plate would be sitting there flat and ready to view. How hard could this be?

A few minutes later and...

It's the black 'pincers' with pale 'shield' that make up the genital plate

I wasn't entirely sure I had the right part, but it looked vaguely like the drawing Julian had sent, along with this sublime line: 

This is what the saltator female genital plate would look like. It's only ever been seen by some of the world's most boring people.

I tried to line it up a bit better for the camera when disaster struck as it pinged across my desk and disappeared into who knows where. Bearing in mind that the entire thing is substantially less than a millimetre across, I had little chance of finding it again. Damnation.

Luckily, Julian was happy that this image confirmed my female gnat as Trichocera saltator. He then dropped this rather large bombshell into my lap

That's the one. The top looks good for saltator. The critical bit is the thickness of the neck of the black 'stalk', which is just out of sight. Think it is saltator though.

As far as I know, you're only the second person in the UK to do this dissection!

Haha!!! So I'm officially one of the world's most boring people - result!