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Problem muscids

Submitted by sifolinia on

I've got a series of 5 male and 5 female muscids from Craig Cerrig Gleisiad a Fan Frynych NNR in the Brecon Beacons. They seem to be the same species, based on several shared characters. All the males and a few of the females were hilltopping at the summit of Fan Frynych and at the nearby cairn, with the remaining females captured at the mire in the basin of Craig Cerrig.

However, I'm stuggling to identify them convincingly using Fonseca. I think they're Phaonia, but nothing within that genus seems to fit well - the best match seems to be P. fusca, but I'm disinclined to believe that! The diagrams in Fonseca are not exactly great and I've not convinced myself that my interpretation of the chaeotaxy is right. Please could someone confirm whether I've correctly identified the prealar and supra-alar bristles in the following images (one is annotated)?

Unfortunately, my set up doesn't allow for whole animal images when the specimens are this big, but other characters include:

  • entirely black ground colour, except the end of the femur and the tibia in the females
  • grey dusting on the abdomen leaving paired black spots on T3 and T4
  • no differentiated presutral acrostichals
  • 4 postsutral dorsocentrals
  • no setulae below the level of the strong bristles on the scutellum
  • mouthedge not protruding
  • arista long-plumose, about 2/3-3/4 the width of the third antennal segment
  • hind tibia without posteroventral bristles, but with one to several distinct posterodorsal bristles (more in males)

Since this isn't the first time I've had trouble with Fonseca's key, is there an affordable alternative for identifying Muscidae? I'm not averse to working with keys for other areas, but I'm not sure I can justify the £200 price tag of something like Gregor et al!

Comments

Tried out the panorama function that I didn't know existed in my photo editing software. It works rather well, so I now have an image of the whole beast.

Thanks for the tip Tony.

Now the challenge is to work out why I didn't think they were Helina and what I was getting wrong, having taken them through the generic key several times! I found another Helina on the same site/day and had no problem getting an ID I was confident in (H. evecta).

Whilst I'm a novice with flies, having only recorded about 250 species so far, I'm not a novice with keys, but I do find that key challenging!

BTW, was my interpretation of the bristles correct?

I feel your interpretation of the bristles was OK, but I confess that I don't always find identifying these bristles easy.

It can be tricky with Helina - they do sometimes have posterodorsals on the hind tibia which look a bit like Phaonia, and the pre-alar is not always very strong, but it looks like your specimen has 2 + 2 sternopleurals (katepisternals), which is uncharacteristic (if it occurs at all) in Phaonia.

It does indeed have 2 + 2 sternopleurals. Thanks for the advice - I'll bear this in mind in the future.

I'll update once I've had chance to look again at the specimens.

All keyed out nicely as Helina duplicata (now reversio), once I got past 13/28 of Fonseca's Phaoniinae key. Thanks to Tony for the pointer and advice, and Howard who contacted me off forum.

I guess it all comes down to the interpretation of those posterodorsals being "much longer than the greatest depth of tibia". Clearly this is not the same as "clearly longer" (which mine are). I'd have more confidence if the posterodorsal length / max tibia width ratio was quantified in the key.

Many muscids can, with experience, be assigned easily to a genus without resort to a genera key. Phaonia and Helina can look very much alike; the distinguishing feature is the presence in Phaonia of a strong posterodorsal on the apical third of the hind tibia. This bristle is lacking in Helina. Posterodorsals on the basal third of the hind tibia are irrelevant here.