Platycheirus albimanus query

[Dillybythesea]

I've just come across some great pics of various Platycheirus species, and the comment that P. albimanus only has three pale patches (in the pattern on the abdomen) and wonder if this is conclusive when faced with a P. albimanus-ish individual, or there are other Platycheirus species where the final tergites are dark/ shiny and lack the final pale patch? Thanks for any help.

[Geoff F]

There are quite a few other members of the Bacchini tribe who don't have coloured patches on tergite 4; or have variable amounts which can be hidden by the camera angle, etc.

And beware of strange light effects which can make some other species with yellowish spots appear somewhat silvery. While some silver spotted species can have spots which take on a bronze hue at times.

However, if you can be certain that your individual really does have silver spots there are only a few possible alternatives to consider, and they should be noticeably smaller.

P. ambiguus is probably the most problematic. Males do have a distinctively different front leg. This species is one of the few Bacchini where the male doesn't have an expansion on the front tibia/tarsus; but getting good photos of this difference can be challenging. However the smaller size should be noticeable.

The others are P. discimanus where males in particular are rather similar in appearance apart from the front leg difference (a much shorter expansion) and smaller overall size. And P. sticticus which seems to be an uncommon and rather smaller hoverfly.

Incidentally, recently I had a Platycheirus species flying near me and landed on a flower. From my initial observation, the spots seemed a touch on the yellowish side so I was wondering if it was P. peltatus or scutatus. But when on the flower it kept it's wings firmly closed so any spots weren't visible.

Fortunately it settled down to feed and allowed me to take some good close photos which included the front leg (it was a male). When I reviewed the images on my computer the answer was perfectly clear. It was P. albimanus.

[JRsbugs]

Hi Rhona!

This is a female Platycheirus scutatus. The first set of spots are sort of comma shaped and smaller, the others usually have a slanted top near the tergite sides and are a light orange colour. Face is well dusted and flattish.

P. albimanus is a strange one, it is supposed to have 3 sets of spots but I often see named examples with a fourth smaller set nearly joined. I am always looking to see what else they could be, we have some which are very similar! I'm quite sure I have other similar species but you need to check other features to separate them, this needs keys. One I had recently was one of these confusion species, I could say it wasn't albimanus due to the size of T3 which should be about 2 times wider than long where on mine it was 1.5 times as wide as long. The spots colouring and most of the description fitted Platycheirus ramsarensis, a very small one which I feel certain I had earlier. You won't find photos (other than mine maybe ) as it's not a common one.

[Dillybythesea]

Thanks Geoff. That's a very full answer and will give me all kinds of directions to explore in the morning. Certainly I wasn't convinced that the silver spots were silver. Several shots looked tea-stained! So where does that take me I wonder - perhaps P. peltatus or scutatus, I infer from your reply? Meanwhile I'm hazy on size, and also need to research the bearing of that. In my mind's eye this one seemed about 6mm. Actually the most distinctive thing today was its static hovering - just superb - but possibly because it's less gusty. Anyway, thanks again! Rhona

[Dillybythesea]

Thanks Janet! Yours came in while I was replying to Geoff! That sounds wonderfully definitive, and I think was what Geoff was gently hinting too! As ever I'm extremely grateful, not just for the ID, but the tips on how it's done!

[Geoff F]

Here is one of those recent P. albimanus male photos which clearly shows the distinctive front leg.

Note the shape of the expansion. Particularly the width of segments. Also, the shape and colour of hair on the femur is distinctive.

[Dillybythesea]

Thanks for that Geoff. What a great shot, and perfect for demonstrating your point about the enlarged section of tibia/tarsus. If I understand you correctly, several species have expansions on the front legs of the male, and identification depends on the shape and nature of it, as well as hair colouring on the femur? (Sigh!) (I'm still wanting it all to be much too simple - eg I'd have taken one look at those stray thickened hairs on the femur and just put scutatus. Groan.) But I shall enjoy looking up those other species you mention - even if it does make my head swim!

[JRsbugs]

P. scutatus has a much thicker tuft of hairs on the tibia, besides other differences such as the shape of the tarsal segments in particular the second segment which is much narrower. The hairs on the back side of the femur are also different.

Here's two from last year showing both these well well on scutatus, the thickened hairs on the femur are more bent than in albimanus as well as having more of the longer single hairs dispersed through the short ones.

[Dillybythesea]

Wow Janet! Such great shots of those features, as well as capturing the whole insect! And thank you again, muchly, for the info and illustration! Rhona

[Geoff F]

If I understand you correctly, several species have expansions on the front legs of the male

Virtually all Platycheirus males have some form of expansion on their front legs. P. ambiguus is the exception; plus a couple of others which are obviously different and should be instantly recognisable for other reasons.

British Hoverflies (Stubbs) has some excellent drawings of the various leg differences.