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Dear all

Apologies for carrying another forums debate to here, but there has been a long discussion underway in a thread on wildaboutbritain about distinguishing these two species, and one of the central characters in the debate suggested posting pictures here for confirmation of their identification. I can see the source of confusion and I have a view on which species it is but am remaining neutral at this point.

Please could someone look at the two pictures attached, they are not my photos and are of the same individual. If anyone fancies sticking their neck out and identifying which species it is, that would be appreciated.

Many thanks in advance, if this isn't the done thing I apologise and will remove this post.

Regards

Bill

That is a male brown argus. The fact it is male and brown is sufficient, even if other characters were not visible. But on the underside the position of the two uppermost spots in the pd series is also definitive, as are several other features (lack of cell spot, chequered fringe, discoidal spot on upf &c.). No need to stick a neck out! It's brown argus!

Guy

Hi Bill,

The pointers are Brown Argus (hind wing cell spot alignment, no forewing underside cell spot, slight chequered fringe) but I have never seen one with any blue on it...

I'd go for Brown Argus but would welcome more opinion! EDIT - I can see Guy already has replied

Cheers

Lee

Hi Bill,
It's a Brown Argus - of that there is no doubt whatsoever, the spotting pattern on the underside being entirely diagnostic. I imagine the atypically blue colour of the thoracic hair has caused some confusion.
Neil

Thanks all, you've completely confirmed my opinion that it was definitive Brown Argus and that it was male .

The cause of the dispute is the amount of blue shown on the upperside of the individual. The blue present in Brown Argus seems to be associated with the hairs on the thorax/abdomen rather than with the wing (the wings on the fresh ones I've seen occasionally have a metalic green appearance). How unusual is it for that amount of blue to be evident in a BA? Is the blue more evident in photos than in the flesh for some reason? For info the presence of blue has been taken as the key indicative feature (it has blue therefore cannot be BA) rather than the fringing, absence of spot and colon on the hind wing being the positive BA discriminators.

Many thanks

Bill

Hi Bill,

The 'no blue' rule applies to the scales only, rather than any blue colouration of the thoracic/abdomenal hairs and the very fine hairs that extend out over the inner wings, or any blue colouration resulting from the diffraction of light - which is a function of scale microstructure. In this respect, like other members of the 'blue' family, the play of light across the wings can have a profound effect on the colours/shades we perceive, despite it being brown in colour. The image below shows a Brown Argus' wings showing greens, bronzes, purples etc.
Going back to the hairs, which are more relevant in this case, the image below shows the detail of a female Common Blue, clearly illustrating both blue wing scales near the thorax/abdomen and fine, blue hairs over the inner wing areas. Your image shows the effect produced by these fine hairs, particularly at the front of the insect, where their limit is clearly defined.
How common is it for so much blue to be evident in a Brown Argus? Not particularly. Obviously-blue thoracic/abdomenal/wing hairs are, in my experience, restricted to male butterflies (as Guy points out - this is a male), and from the thousands of specimens I see each year on the Downs, where it's a very common species, I would say that similar examples certainly make up less than 5% of the population. This might well vary around the UK. Despite being unusual, this buttefly falls within the range of natural variation for the species, and colouration of these hairs can't ever supercede the clear diagnostic features that 'define' Brown Argus (as listed by Guy).

Neil

Sussex Kipper wrote:Hi Bill,


Neil

Marvellous thanks so much for that Neil,

Bill

Hi Bill,

If in doubt do not rely upon the absence of the cell spot on the forewing underside to determine identification; it is not at all uncommon for Common Blues to lack this feature.

Felix.

Felix wrote:Hi Bill,

If in doubt do not rely upon the absence of the cell spot on the forewing underside to determine identification; it is not at all uncommon for Common Blues to lack this feature.

Felix.

Thanks for that Felix, I take it that the absence of the cell spot on the forewing underside together with the colon or 8 on the hindwing underside is definitive though?

Bill

The presence of a cell spot is definitive, in the sense that brown argus never has one. It's absence, as Felix says, is no more than a pointer. After you've got your eye in on a handful of carefully identified butterflies, though, you won't need pointers or identification criteria ever again. The butterflies are as different in the flesh as crows and blackbirds!

Guy

Hi Bill,

For the benefit of some readers (who might not be aware of exactly what a 'cell spot' or the 'colon marking' is) it might be worth looking at Steven Cheshire's pictorial guide at http://www.britishbutterflies.co.uk/com ... ow-res.pdf

In summary:
1) The 'colon marking' is the one feature that really will suffice for those that find differentiating the two species initially perplexing. This is circled 'b' in Steven's comparative image.
2) The 'cell spot' is NEVER present in Brown Argus, but USUALLY present in Common Blue. This is circled 'a' in Steven's comparative image. Bearing in mind that the forewing is sometimes 'folded' behind the hindwing, obscuring this feature, it really is best to concentrate on the 'colon'!
3) In a small percentage of male Brown Argus, there may be blue hairs over the thorax and abdomen, and fine blue hairs over the inner areas of the wing - but there are no blue wing scales.

I hope we haven't made this appear too complex. As Guy says, once you get 'your eye in' it's a 'crows/blackbirds' situation.

Neil

hi bill,

to further illustrate the confusion with lacking cell spots heres a pic of a female common blue i took today that i had to look twice at.

gary

Hi everybody,

Without wishing to complicate things further, but worth mentioning is that occasionally the colon feature is missing. I think it can happen particularly with Northern Brown Argus. Here is a photo of a female taken at Arnside Knott last July.
Vince

When I was a youngster I always used to look for the over all 'shape' that the underside hindwing spots make: in the Common Blue it is always a capital 'D' shape. This is never the case in the Brown Argus, even when the 'colon' is missing.

Felix.

hi felix,

is there a specific name for the common blue aberration without the cell spot?

gary

Hi Gary,

Yes, but I can't remember what it is..! Curse my addled gray matter. I shall look it up...

Felix.

I saw the first Common Blue I had seen without a cell spot this year too, at Aston Rowant NNR.
Cheers
Lee

Felix wrote:Hi Gary,

Yes, but I can't remember what it is..! Curse my addled gray matter. I shall look it up...

Felix.

Icarinus!

Guy

thanks guy,

oh dear felix, it only gets worse as the years go by, take my word for it.

cheers gary.

Thanks all for the further discussion points, and the link to Steve's article. All very useful

Cheers

Bill