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Here's the underwing of the butterfly of disputed identity (reference my entry in the June competition) photographed at Grass Wood in Upper Wharfedale. Is it NBA, BA or a hybrid?

I would say it is a Male Brown Argus.
I have concluded on this by the lack of orange on the upper fore wing and the black in the large spot on the under side of the fore wing.

Cheers Andy

I've just re-read the relevant section in "The Butterflies of Yorkshire" edited by Howard M Frost (ISBN 0954824903), which was published in 2005 and is therefore pretty much up-to-date. It's clear that even the experts have at times puzzled over the distinction between NBA and BA, but let me quote briefly from the ID notes on page 129, which are based on extensive studies:-

"...the range of variation (of markings) means that individuals cannot be cited as having diagnostic features either in Yorkshire or elsewhere. For the time being, identification is best made on a geographical basis: we can say that...populations on the northern Pennines are Northern Brown Argus (probably hybrids.)"

I think this shows conclusively (as near as dammit) that the butterfly in question is not an "ordinary" Brown Argus.

The upperside and underside pictures strongly suggest a hybrid to me. The markings generally indicate agestis but the wing shape, with its very flat, even concave costa and pointed apex, gives me the feel of artaxerxes. This distinction is less obvious in males, however (which this is), because male agestis can sometimes be quite angular too.

As I have never seen British artaxerxes I'm not prepared to go further than this!

Guy