Northern Brown Argus in Smardale

[PaulK]

Hello

Although I've been dipping into this site for a few years now, this is the first time I've been confused enough to ask a question!

I was in Smardale (East Cumbria) a few days ago for the Northern Brown Argus. I must have seen 100+ specimens and photographed perhaps 20 or so.

Although I'd never seen this butterfly before, I'd done quite a bit of reading up and I was pretty confident I knew what I was looking for. In particular I'd been led to believe that there were two spots on the leading edge of the underside of the rear wing forming a colon. The clearest example I managed to photograph is attached as photo 1. In most of the other specimens I saw the inner circle was generally smaller and lacked a black centre. As I've seen similar photos of NBAs elsewhere in this forum I guess this is nothing special.

However, I found several specimens in which the inner circle of the colon was missing (or perhaps displaced), as shown in photos 2 and 3.

When I got home and had a closer look through my books I found that this type of patterning was actually included in one of them and designated Fsa (Britain's Butterflies, Tomlinson and Still). Presumably this means a female of the salmacis race. Would it therefore be correct to infer that all salmacis females have this characteristic? There is no mention of this in the accompanying text as a means of telling the sexes apart though, and so perhaps it was just a coincidence.

Some clarification would be appreciated!

Thanks in anticipation.

Paul

[PaulK]

To answer my own question (I think):

I've since had a look at the photos of the Brown Argus included in the book previously mentioned, and both the male and female specimens photographed show the same colon arrangement of the spots half-way along the leading edge of the rear wing. As I understand it, the Brown Argus and Northern Brown Argus are very similar species, and are difficult to tell apart from appearance alone (range being a better indicator). It would therefore seem to be unlikely that the underwing patterning is indicative of sex in one case but not in the other. So I guess it was just a coincidence that the female salmacis NBA illustrated in the book was missing a spot.

I'll get my coat...

[Mikhail]

Paul, I have just looked at my copy of Butterflies by E.B.Ford (the first in the New Naturalist series). Plate 45 shows artaxerxes, agestis and what Ford calls the hybrid race (salmacis). Interestingly, two of the three undersides of salmacis lack the lower spot of the colon and in the third it's reduced to a tiny white dot. You may be on to something, and possibly this reduced spotting is particularly characteristic of salmacis.

Misha

[PaulK]

Thanks for that info, Misha.

I think the illustrations in your book are a better match to my observations than the illustrations in my book! In Tomlinson and Still the lower spot is either missing entirely (I saw several of this type) or of the same size and clarity as the higher spot and with a black centre (I didn't see a single specimen like this).

For the record, I've attached a few more photos which are pretty typical (from memory) of the "two spotted" variety.


Paul