www.ukbutterflies.co.uk

I have posted this picture



to Biolib.cz as "Plebejus argyrognomon". But an expert of Biolib has noted that "Perhaps it is Plebejus idas, which flies obviously from June to August, this year perhaps later - from July. Plebejus argyrognomon has had the first breed late on June this year (caused by the cold spring) and the second one would be on August."

If it is really idas then it would be a meaningul find because idas is near extinct in the Czech republic while argyrognomon is common on appropriate places in the warmer areas.

Is it posible differ from these photos or this video?

http://www.youtube.com/watch?v=Q28c3EbvYfA[/video]

When I watched that video for the first time, before your most recent post, I also noted that it looked more like idas. I didn't say anything because a view like this cannot be definitive and I presumed there were other reasons for your knowing this was argyrognomon.

To determine definitively, without butchery, you need to do a little field work and find out what she's laying on. The females of both species remain relatively close to their foodplants, in my experience, so I would go back there, and watch, and wait!!

Guy

Thank you Guy! My only reason for "argyrognomon" was that idas would be a rarity.

They certainly look rather like idas, but I would go for argyrognomon for two reasons: 1) the marginal orange band is contnuous and reaches the unf apex whereas it does not in idas, and 2) the external surfaces of the black edging to the lunules is relatively flat whereas I would expect it to be significantly more sagittate for idas.

Also the colouring of the female looks good for argyrognomon.

Here is a female argyrognomon I took (a photo of) recently.

Like me, Roger relies quite a lot on jizz for argy and idas, because in the field argy is really quite distinctive (at least in the populations we know). But when you start trying to put your finger on constant differences it can be tricky.

This is definitely idas - it was in Sion, in the town, and argy has never even been recorded in the Rhône Valley:



Nevertheless, the forewing orange band is wide and the orange reaches to the apex. So while agreeing argyrognomon is perfectly possible for your insects, Traplican, the extent of orange does not rule out idas and I definitely think it worth revisiting the site and trying to make sure. There are several features of the female in particular which put me just on the other side of the fence from Roger, but not so far away we can't shake hands and agree on most points!

Guy

That looks like argy to me Guy.... maybe you found a colony

Wishful thinking, Paul!

It's definitely idas, but it does show how some superficial criteria can mislead on occasion.

Guy

I suddenly remembered a very useful criterion I only learnt a couple of years ago but have never had to use because in Switzerland the two species occur in quite different places.

Female idas has brown fringes (the hindwing fringes are particularly diagnostic), as shown quite clearly in the picture I posted above (you, see, Paul, it was idas!!). Female argyrognomon has white fringes.

Here is a couple of idas, showing the brown fringes in the female:



Here is argy female, showing the white fringes:



That makes yours argyrognomon. Still worth checking, but I've now changed sides to join Roger...

Guy

White flag!

Thank you, Guy!

I have restored the folder with the photos from July 23th from the "recycled" basket and processed all photos with focused fringes of the female's hindwing. Apropos, this is why I always take more photos of the same object and hesitate to fling them away if at least a part of object is focused: Maybe this is just the part with differentiate criteria which I don't know but which knows an expert.

All photos with focused margin of female's hindwing are placed into the album now.
It seems to me that the female has white fringes on the hindwing, exluding : and After these markings: Is it soon argyrognomon or idas?

P.S.:

Now I have compared these photos with ones from June 12th and noted that on the photos of argyrognomon female from June 12th the frontal white fringes far overlap the first orange spot while by the female above doesn't achieve the front margint of the most frontal orange spot:

Without studying the full range of variation in each species it is difficult to know how much weight to put on the various criteria. You obviously want these to be idas, as it is fantastic to discover something rare like that, but unfortunately I don't think you'll ever get sufficiently convincing proof just from these photos! If idas does really fly there you should be able to find more individuals and observe their behaviour, their attraction to various plants and so forth. Ideally, as I said, you will be able to watch a female laying. I think this is how you will prove the butterfly flies there, if it does.

In Switzerland, argyrognomon is a butterfly of low-lying meadows with long grass and plenty of Coronilla varia. Idas is either a mountain butterfly or, where it flies in the valley, is associated with sea buckthorn. The context and the circumstantial evidence are in all cases I know sufficient on their own for identification, though I do find the butterflies look very distinctive in the field too.

In short, I think you need to go and get more data!!

Guy

Foodplants of P. argyrognomon in the Czech Republic after http://www.lepidoptera.cz/index.php?s=motyli&id=99 are:
- Purple crownvetch - Coronilla varia
- Wild Liquorice - Astragalus glycyphyllos

Foodplants of P. idas after http://www.lepidoptera.cz/index.php?s=motyli&id=98 are:
- Black Medick - Medicago lupulina
- Red Clover - Trifolium pratense
- Genista pilosa
- Broadleaf Birdsfoot Trefoil - Lotus corniculatus
- White Sweetclover - Melilotus alba
- Kidney Vetch - Anthyllis vulneraria
- Common Broom - Cytisus scoparius.

Both species often occur on the same places but P. idas is much more local and rare.

OK - Switzerland 8th July 2010. 1800+m Argyrognomon - Reverdins Blue -(Edit Idas Blue ) not great shots but you can see the ups and uns of the same individual...not as many blue/green highlights, at least on this individual, as idas; and perhaps the male is greyer than the idas...? Not sure it helps in your case....
(Edit - Definitely not!)

There is a difficulty that the shade may depend on the wear of the butterfly, on the lighting, etc. Better idea is to compare shades of one part of the specimen with another part of the same one. For example if the fringes on the frontal margin of hindwing before the first orange spot are white by the argyrognomon female, consequently they are plain on the background of the forewing backside while by the idas they have the same shade, then it would be good differential marking. There would be good relatives for comparison: The position of the first orange spot of the hindwing backside and the shade of the forewing backside.

NickB wrote:OK - Switzerland 8th July 2010. 1800+m Argyrognomon - Reverdins Blue - not great shots but you can see the ups and uns of the same individual...not as many blue/green highlights, at least on this individual, as idas; and perhaps the male is greyer than the idas...?

That's idas, Nick. Moreover, it's classic, and shows perfectly the upperside jizz that makes the males look very different in the field!!

Guy

OK thanks - I'm used to this now

... the way the black intrudes into the white border on the hind-wing looks more like argyrognomon....
....and the male in Tolman looks browner rather than greyer on the underside....
..though I read now that at altitude the number of blue/green highlights on the hind-wing is diminished in idas...
Back to your mantra - ID in the field!
N

Yesterday I have visited the site and taken the butterflies, especially Silver-sudded/Idas/Reverdin's Blues here (grassy place with shrubs cleared only), here (abandoned grassy orchard growed by the bush over) and here (the pasture).

I have noted these possible foodplants of Plebejus sp.:
- Purple Crownvetch - Coronilla varia
- Wild Liquorice - Astragalus glycyphyllos
- Red Clover - Trifolium pratense
- Broadleaf Birdsfoot Trefoil - Lotus corniculatus

Wild Liquorice was completely past blossom, with ripening pods. On some pods there were some outgrowths (and the 2nd one), probably caused by insects.
Purple Crownvetch and Red Clover were past blossom, to, but not completely and I have found some flowers of ones.
But the flowers of Broadleaf Birdsfoot Trefoil were what the Blues were most attracted by. But I haven't succeeded in taking of any female putting eggs.

I have taken a collection of photos with extra consideration to P. idas/argyrognomon of which I have taken more specimens and mostly more photos of each specimen.

By some females of ones it is difficult to differ if they are P. idas or P. argus.

P.S.: My photo on Biolib.cz was re-determined by Jiří Beneš from the Czech Entomological Institute back to cf. P. argyrognomon with the remark: "Near surely it is not P. idas, the 2nd breed of P. argyrognomon occur in south Moravia as early as from the half of July, for example in areas of Chřiby hills or Ždánice forest is abundant (and many times revised). Species Plebejus idas is badly determined practically in all collections - incl. museum ones, nearly always it is P. argyrognomon, P. idas is clearly near extinct in the CZ now - and its exigencies are much more clean-cut. On principle I don't recommend determination after the habit of the imagos, such determination wouldn't taken seriously, the audit of the prove specimens after male genitalia is absolutely necessary."