Diptera.info

Posted by blowave on 20-08-2010 21:23

Hi,

The only one I can find which has a front tarsus swelling like this is Platycheirus amplus. It certainly is ample!

But it seems this species has only been found in Scotland so far, and with very few records at that.

I can't find any pics of P. amplus, but it is supposed to resemble P. peltatus in the spots as one in historic records was mistaken for that.

Help me please, I am going mad. :o

Taken in my garden south of Lincoln UK on 16th August. I am in a woodlands and heathlands type location, it was feeding on Veronica which is near my pond and not far from a roadside drain.

I have two pics, posting a third crop of the front end.

Janet :)

Edited by blowave on 22-08-2010 22:53

Posted by blowave on 22-08-2010 22:51

Gerard, I had at least one P. peltatus in my garden most of the day yesterday so I got a lot of pics.

I wonder if you could look again at the shape of the swollen section of the tarsus. To me, the shape is quite different to what I see as peltatus. The bottom line of the swollen section in peltatus is a continuous curve, where on my fly it looks to curve upwards in a 'u' shape towards the point. There are other subtle differences too.

As you thought the female Platycheirus I had could be P. nielseni, I wonder if this male could be too. I can't find anything at all about nielseni, not even a drawing of the tarsi.

I now also see that P. amplus has a continuous line at the bottom of the swollen section, and a more blunted point.

I was searching for P. neilseni and found an old thread here, where Andre had suggested either P. amplus or neilseni for a fly which looks to have the same shape tarsus as mine, I think!

http://www.dipter...pid=119033

Once more I am thinking this is :S :o

This pic is of P. peltatus I believe..

Posted by Gerard Pennards on 23-08-2010 09:04

Hey Janet,
Well, I can tell you that peltatus and nielseni cannot be separated by using only the first leg. The explanation is simple: these first legs are identical! Identification between males of these species is made by looking at the shape and the hairs on tibia of the second leg. In nielseni the shape of this tibia is slightly different from peltatus. The assumption is generally made that peltatus is commom, whereas nielseni is rare in England.
In sweden it's a different story, nielseni is more common and there are some other species of this group as well!
Greetings,

Posted by blowave on 23-08-2010 13:43

Thank you Gerard for that information!

Now I think then that the first one cannot be P. nielseni, as the shape of the swollen section on the tarsus is different to the second fly which does fit P. peltatus (or nielseni) well. But as you say, nielseni is more rare.

I do have flies in my location which are much rarer than P. nielseni though!

Where does that leave us? :|

Posted by blowave on 23-08-2010 20:38

I have a tibia #2 pic from the last fly :D

From the drawing I have looked at of nielseni tibia 2, this looks like it could be that. It would make sense if I have a female which looks like nielseni too.

Does the eye of experience think so too? :)

picture didn't go in..

Edited by blowave on 23-08-2010 20:39

Posted by blowave on 23-08-2010 20:40

#10

couldn't add the pic with an edit so trying again..:|

hmm, I see the pic flash up before my eyes but it doesn't show. Maybe I will try later.

Trying again..

Edited by blowave on 24-08-2010 00:22

Posted by conopid on 24-08-2010 13:13

#12

These flies are hard enough to decipher with a specimen under the microscope, so as Andre' says the best thing to do is forget determining the species from a photo. That way it won't drive you mad any longer!

It's always worth collecting specimens if you really must know the specific identity of a fly in the genus Platycheirus.;)

Posted by blowave on 24-08-2010 13:58

#13

Lol, that's about what I thought Andre.

Nigel, I can't help but try to find what I have even if it drives me mad! I can't do the collecting thing though. :|

At last while I'm looking I'm learning, and that can help with the more obvious ones.:P

Well I will still try to post my pic anyway, for the record! Here goes..

(it flashed before my eyes again, this was not meant to be! :S)

I just realised, because I had a pic within size limits I had forgotten to rename it without capitals etc!

Edited by blowave on 24-08-2010 14:03

Posted by blowave on 24-08-2010 16:18

#15

conopid wrote:
Nope, I can't do it from that. You'll have to train them to pose with legs held out in the right positions:D

Oh, but can't you tell I have already done that? :P

Description (and drawing) of P. nielseni tibia from Van Veen, I hope I'm not out of place putting this here but it does illustrate it well I think.

Constriction on tibia 2 profound and about 1/3 the length of tibia, preceded by a swelling and ending in a strongly swollen apex, upper part of swollen apex with a tuft of longish hairs.... P. nielseni

Description of P. peltatus..

Constriction on tibia 2 shallow and about half the length of tibia, preceded by a swelling and ending in weakly swollen apex, this apex only with short erect hairs;..... P. peltatus

Pic of P. nielseni tibia drawing..

Edited by blowave on 24-08-2010 16:19