Blue ID please

[George]

I took this picture in Cornwall on the 6th September at Tintagel on the cliff top. It has been puzzling me for ages because I assumed it was a female Common Blue but after looking at it again the spot on the forewing that is one of the clues for a blue id is missing. I had wondered if it might be a Silver Studded but the hind wings do not look like one of those either. Please help!!

[Pete Eeles]

I reckon this is a Brown Argus. A similar shot is at:

http://www.ukbutterflies.co.uk/image.ph ... May-04.jpg

Which reminds me that I must get the ID "tips" sorted out this winter

Cheers,

- Pete

[eccles]

The missing dot on the forewing that is present in a female common blue makes a brown argus my guess too. I think the colour suggests a female.

[George]

Thanks for that. I wasn't expecting a Brown Argus answer or I would have also shown you the the upperside of the same butterfly. Do you still think it is a Brown Argus? There is some blue near the body which I didn't think was present in a Brown Argus.

[Pete Eeles]

Hmmm. In that case, definitely not a Brown Argus.

So I'll "default" to a Common Blue aberration. The spots on the undersides are, according to the literature I have to hand, quite variable in terms of the size and number of spots.

If you take a look at the Cockayne database, you'll see some examples of such aberrations.

http://internt.nhm.ac.uk/jdsml/research ... IES=icarus

Cheers,

- Pete

[eccles]

I wonder if it's not still a brown argus. I've seen irridescence in the hairs on and around the body before, but you'll notice that there are no blue scales at all on the wings. At least what wings remain.

[Roger Gibbons]

There is one sure identifier between icarus and agestis undersides: in agestis the unh postdiscal spot in s6 is out of alignment with those in s5 and s7 – it is usually quite close to and just below the spot in s7. In icarus, they are in a smooth curve as in this photo.

[eccles]

That sounds quite a useful identifier, Roger, at least it would if I understood it. Can you translate into simple words please? I've worked out that agestis = argus and icarus = common.
Looking at the upper wing shot again, there is just too much blue there for brown argus so I stand corrected by both Roger and Peter.

[Roger Gibbons]

On the underside hindwing there is a series of nine or so white-ringed black spots in a strong curve, almost a horseshoe shape or sometimes even an L-shape. Starting from nearest the head, the third one along is clearly out of line with the others in brown argus, which means this butterfly isn't a brown argus. The absence of a cell spot on the underside forewing is a bit confusing, though. The cell spot can be very variable in size, but I’ve never seen a common blue with not even a vestigial cell spot. I still think it must be a common blue, though.

If you have a look at the underside shots on the common blue and brown argus pages on the UK Butterflies species pages, it is a lot easier to see.

I hope this helps.

[eccles]

Got it, thanks!

Here's the two species, and as you say the spot arrowed is aligned in CB but not in BA.

Common blue...


Brown argus...

[MattRowlings]

Roger's underside ID clue is an absolute boon when confronted with a roosting butterfly or a photo (where obviously one cannot expect the butterfly to move to view the upperside...). The cell spot is absent in Common Blues as an uncommon but apparently constant proportion of butterflies so the lack of a cell spot does not automatically mean Brown Argus - Roger's wonky link does mean Brown Argus.

[hjalava]

Differences between Common Blue and Brown argus: http://www.glaucus.org.uk/BflyBlues03.html