Ain't Nothing 'Lesser' about this Dungfly!

Here on Skye, the Sphaeroceridae are a commonly encountered bunch of flies. By and large they are tricky blighters to identify, being mostly small flies clothed in various shades of black. Exotic they ain't. Or so I thought.  Here's the relevant section of Stuart Ball's Diptera Family Descriptions

The difficulty rating for fly families tops out at 4, these are rated 3-4. I figured Sphaeroceridae were essentially beyond mine and my microscope's abilities. I mean, just imagine checking the orientation of orbital bristles or doing a gen det on a fly that rocks in at 0.7mm! But yesterday I swiped what was, according to my notebook entry, an "ugly black fly walking around on leaf". I remember it well (it was only yesterday after all...) a flattish, hairy thing that put me in mind of a Kelp Fly (Coelopidae). Except I was in the middle of deciduous woodland nearly half a mile from the sea. It was walking around and around a Tutsan leaf, saw me and scurried to the underside, then back up again. I netted it directly from the leaf before it could fly away, though I suspect it would probably have simply fallen to the ground rather than fly off. I pinned it last night and only checked it this afternoon after another failed Yellow-browed Warbler hunt. 

Beneath the microscope I quickly guessed it was Sphaeroceridae, the obviously enlarged first segment to the hind tarsus being the giveaway feature. I ran it through Oosterbroek anyway and it did indeed drop it out at Sphaeroceridae. Cool, I actually recognised it correctly. Here's a pic of the beast on a pin

Two things stand out with this fly. Firstly the enlarged first segment of the hind tarsus. Secondly, there's a bloomin' great hook on the underside of the hind femur. Plus, as far as Lesser-dungflies go, it's a real giant. I measured it at 5.5mm long, that's the absolute maximum size for any member of this family. I fancied my chances with this bad boy, so reached across for my copy of the RES Handbook.

I keyed it through and soon went wrong. Like definitely wrong. Hmmm. I couldn't see where I'd erred until about the second or third subsequent attempt. I was entirely happy that I'd keyed it correctly in the subfamilies key (to Copromyzinae) but from there I kept getting sent to Borborillus, which it wasn't. Suddenly I realised I'd gone wrong at the very first couplet due to thinking I knew what I was looking at rather than checking properly. Dingbat, will I ever learn?

It's a rubbish image, but it proved surprisingly difficult to show you what I wanted (so difficult that I didn't 'see' it properly for myself the first couple of times I keyed this feature!) Look at the bristles behind the eye, plus on the back of the head itself. The key asks if these are in one row or two. At a quick glance I repeatedly saw one row just behind the eye. But actually, you need to count the ones behind this row too. And that's where I kept going wrong. Once I'd overcome that minor fiasco, it was actually very easy. 

There are lots of good ID clinchers in this one image

Wing venation also helps clinch the ID

A (very) shortened version of the "Key to genera and species of Copromyzinae" now follows - 

1) Postocular setae in a single row or at least two usually irregular rows? Well now we know... >>11

11) One or two setae on postpronotal lobe? Scroll back up to the second fly image and count the big bristles on the "shoulder pad". Just one, not two. So >>12

12) Wings greatly reduced or full. Obviously they're full  >>13

13) Hind tibia with or without anteroventral bristle at about the middle?

Nope, no anteroventral bristle at or about the middle of the hind tibia >>14

There are several parts to Couplet 14 so I'll tackle them individually. 

14a) Anepisternum part shining or mostly shining? Scroll up three images to the one where I say there are lots of good features. The anepisternum is the flat 'body panel' that has the pin sticking through its extreme bottom right corner. You can see that the front, bottom half of this 'panel' is black and shiny, but the top and rear edge are matt. So I'd go with part shining as opposed to mostly shining. 

14b) katepisternum with 2 or 3 close-set, very long setae, or not? Scroll up to the same image again (sorry!) and just in front of the pin you can see a couple of pale wispy things that extend to just beneath the pin. These are actually three long black wispy hairs, they've just happened to catch the light which makes them look very pale. So yes, there are 2 or 3 long setae present. 

14c) Male with or without a large tubercle at base of hind femur? You can clearly see the 'hook' (or large tubercle as the text states) sticking out from the base of the femur. 

At this point we either drop out at a species, or continue on through more baffling terminology. Happily, this is where we drop out to species. 

"Anepisternum part shining, katepisternum with two or three close-set, very long, setae. Male with large tubercle at the base of the hind femora. Very large species (length 4.0-5.5mm).... Crumomyia nitida (Meigen)."

Just to smash home that I have the ID correct, the first line of the description reads, "In woods, running over leaves....." Ha, that's precisely what I wrote in my notebook. Only I added "ugly black fly", but I guess the author of this particular handbook would probably disagree with that sentiment. 

This is the first sphaerocerid I've tried to key through and, minor issues with postocular setae aside, it wasn't at all tricky. To be fair, I suspect this is one of the easier species to identify. I did a bit of online researching and found this rather brilliant page which clearly shows all the features that my images claim to show. A quick peek at the NBN Atlas shows that it occurs up here too, always a relief when that happens. There's a September 2015 record from Skye itself, hence mine will be the second Skye record according to the NBN. Lots of records in the Inverness area, that'll be Murdo from HBRG. Also a handful of Outer Hebs records, which is always good to see.