unidentified Rhamphomyia sp.

I attempted to use the Mike Hackston's keys to identify this fly, but have run into difficulty. I'm not sure if I've gone wrong or if this individual doesn't conform to the key - any advice welcome! Scroll down for more pics and discussion as to how it keyed.

It keyed straightforwardly to Rhamphmyia genus.

female Rhamphomyia sp. showing wing, North Elmham Cathedral Meadows (Norfolk, UK), 28th April 2021

So, using the Hackston key to Rhamphomyia... Couplet 1: axillary lobe well-developed and axillary angle acute - so to couplet 2.

Couplet 2: Vein bordering upper side of discal cell distinct, and cell relatively short, so to couplet 5.

Couplet 5: A slight hint of yellowish present on the thorax (around the dark stripes), but overall greyish. Certainly can't say "Thorax distinctly yellowish, not black or grey", (but checked online photos of the options that followed from this lead just in case, and no, they're obviously yellowish) - so to couplet 7.

Couplet 7: The legs are dark, so the main decision here is are acrostichal bristles present or absent? I suspect an experienced dipterist would find this a simple question, but I ask myself, when does a hair become a bristle? Are those little things sticking out of the acrostichal region classed as bristles or not? Online photos don't help - they're nearly all from the side and it isn't clear if the top row of bristles are the acrostichals or not. I think they are bristles, but check the rest of the text in this couplet. If acrostichals are absent then the legs shouldn't be pennate... Despite Mike's helpful explanation of this term I'm not quite sure - I don't think they're pennate - I can't see any bristles that look very compressed. That doesn't help though, as it doesn't say the other couplet is pennate, just that the acrostichal-less option isn't. The option without acrostichals should be long-legged, the one with should be stout or plump. This looks quite long-legged to me, but compared to what? I'm not sure which way to go. I favour arcrostichals present, couplet 15, but decide to check acrostichals absent first, couplet 8. If in doubt, check both options.

same female Rhamphomyia sp. showing thorax from above

Couplet 8: dorsocentrals seem fairly weak to me but I'm not sure, and for the stronger option it implies they're weaker on females anyway. But the weak option also requires none of the bristly hairs on sides of prosternum to be pointing downwards, and some of them are (arrowed below). The other option (Rhamphophyia variabilis) requires yellowy-brown legs - they're not. So it seems I was right, they were acrostichals - so go to couplet 15 from couplet 7. Hang on though, what if I've misinterpreted those downward-pointing hairs on the prosternum? Check couplet 9 just in case...

same female Rhamphomyia sp. showing hairs on prosternum

Couplet 9: Too big for the first option at around 4.8 or 4.9 mm from front of head to end of abdomen and not shining black or greyish black. The other option says acrostichals present, which by implication from couplet 7 means legs are yellow, which they're not. Just in case that's a mistake, checks couplet 14.

Couplet 14: One couplet has a yellow thorax with two grey stripes and the other is uncommon in Scotland in August and September. This was in Norfolk in April, so I think that nails that one as the expected dead-end. So, back to couplet 7 and on to couplet 15. Feels better - the option I thought was right, but now ruled out the alternative.

Couplet 15: The labellum is stout and has some hairs that are longer than its width, so it should be the second option here. But this option says the labrum is seldom much longer than the head is deep. The labrum on mine is much longer, like the first option. Well, seldom doesn't mean never, so maybe that's ok. It says in doubtful cases I'm to look for a distinct bristle in 'comb' at tip of hind tibia posteriorly. It says this can be hard to see - I concur! There are a few spines and brisles and frankly I'm not sure if one of them is this or not. But unless I've misidentified the labellum, there really isn't any doubt - it's clearly stout and long-haired. I have a quick look at couplet 16 just in case and neither options look right (no white hairs on the abdomen), so on to couplet 17.

same female Rhamphomyia sp. showing labellum and labrum, and two sides of the tip of the hind tibia.

Couplet 17: There are hairs on the prothoracic episterna if it's the bit I think it is (arrowed below). Also it's a female and it doesn't have the abnormal wing venation illustrated, so another easy one. On to couplet 20.

same female Rhamphomyia sp. showing hairs on prothoracic episterna

Couplet 20: Aha, I've seen Rhamphomyia marginata - it was brilliant, and nothing like this. On to couplet 21.

Couplet 21: The introduction to this couplet suggests it may be tricky and advises using a combination of characters. But they all match the second choice for subgenus Rhamphophyia and couplet 50. The anal vein is distinct throughout, the axillary indentation is acute, the sides of the prosternum have plenty of hairs and the episterna is hairy.

Couplet 50: Looks like a male would be easier here. For a female all I have to go on is whether the palps are projection and strongly bristled or usually smaller and weakly bristled or hairy. I hadn't noticed the palps but there's something with quite long bristles just slightly protruding - is that a palp? Not sure. It's hardly protruding, but it is well bristly. I'm going to have to try both options, couplets 51 and 52, although the first option seems unlikely as it says "Only recorded by Collin from the Highlands of Scotland."

same female Rhamphomyia sp. showing what might be a bristly palp, slightly protruding?

Couplet 51: Larger (6.5mm), blacker species isn't right so of the two it would have to be the second, but that's still too big (6mm). I'm never quite sure which part of the front of the head is included in the "face" so I'm not sure if it's bare or not (its bare in the centre, bristles down the side). The other characters really need material to compare with. So if I am to interpret that thing as being a bristly protruding palp, then it's a very small Rhamphomyia albosegmentata. NBN Atlas has some records south of the Scottish Highlands, but not much south (and none confirmed in England). You never know, but I think it's probably safe to say it isn't this. Interestingly though, I do see an image of this species online that clearly shows a long labrum, so my concerns about this in couplet 15 are alleviated a little. So, we go the other way from couplet 50, to couplet 52.

Couplet 52: The halteres are clearly pale and don't have a darkened knob (assuming the knob is the round broadened bit at the apex, not the base), so to couplet 55.

same female Rhamphomyia sp. showing a haltere

Couplet 55: There's a bit in brackets that says if it's a female the hind femora should have distinct pennate ciliation beneath for the first option, but there's no equivalent comment under the second option, so I assume it could be either way there? Anyway, I also assume that the rest of it applies to both males and females as it doesn't say otherwise, so the presences of distinct black spines under the hind femora send me to couplet 58.

same female Rhamphomyia sp. showing both hind femora

Couplet 58: The decision here is whether the whole of the prosternum is hairy or just the sides. I had to remove the head to get a proper view, and the centre (below where the head was) was bare, so on to couplet 66.

same female Rhamphomyia sp. showing prosternum (head-hole above it and fore coxae below it)

Couplet 66: This one's a problem - seems we may have hit another, final, dead-end. It has brownish wings, at least the veins are brown and there's a faint brownish wash over the wings, strongest near the costa. That fits Rhamphomyia tibialis, but the size is wrong - that's over 5 mm. The other option is more like it, 4-5 mm. Then again, it's only just under 5 mm, and I'm measuring a dried specimen, so maybe it's ok for tibialis? But female tibialis's hind tibia has "very distinct short pennate ciliation". I'm still not quite sure what's meant by this, but I wouldn't have said this is very distinct? The other option requires clearer or milky wings. How brownish is brownish, and how brownish is clearer? I'm not sure. Check couplet 67 and see what that says...

same female Rhamphomyia sp. showing hind tibia

Couplet 67: Rhamphomyia nitidula is the first choice, and it's "shining black, including abdomen." Well it's not that then. Presumably this was the "clearer" wings in couplet 66 as the other option here, Rhamphomyia ignobilis, has "decidedly milk-white" wings. I don't think under any stretch of the imagination you could describe this as having milky-white wings, and anyway this seems to be another Scottish Highland species.

So couplet 67 is a dead-end. I return to couplet 66. Maybe, if very distinct short pennate ciliation means not very distinct ciliation that I can't tell is pennate, then it could be tibialis. But otherwise I've gone wrong somewhere - or the key has. After a lot of effort, the fly must remain unidentified for now. My only hope for resolving this is that with more experience I'll be able to come back to this and figure it out - or maybe someone else will be able to look and tell me where I've gone wrong. Don't you just love flies?