Male Brown Argus or Female Common Blue?

[Lord Adonis]

Hi,

This is my first post as I registered for ID help, thanks in advance.

I’m usually able to tell the difference from the underwing spot pattern but this one has me stumped so I would appreciate any help from those more experienced. This is why I’m unsure – the forewing lacks the clear second spot, which usually means Brown Argus, but the hindwing doesn’t have the “figure of eight” pattern in the two spots, and looks more like the female blue to me. Sorry about the poor photo quality, shot with phone. I have shots of the butterfly with open wings but it was quite old and tattered and didn’t really help me. On site it looked very brown but there are traces of blue in the photos, I know that doesn’t mean much.

The ID is important as it’s part of a butterfly survey I’m involved in at a nature reserve which is full of Common Blues, but doesn't have previous records of Brown Argus. Furthermore the geographical location, a few miles north of the known UK northern limit of the Brown Argus, would support range extension in response to climate change, if a new colony has established here.

If I had to bet cash I’d say Female Blue which has lost the forewing spot with age (there’s a faint mark there), but I want to get this right as it matters.

[millerd]

My guess would also be female Common Blue. There is a vestige of the spot on the forewing, and the hindwing pattern is that of a Common Blue. I came across one the other day that completely lacked that forewing spot, but was definitely not a Brown Argus (it was noticeably blue!). If there was any blue at all, it's not a Brown Argus.

Dave

[bugboy]

I agree with Dave. It's not uncommon to find blues with missing spots but the arrangement of existing spots is much more consistent to the species. If it were me I'd have little doubt in saying this was a Common Blue.

[Lord Adonis]

Thanks that's how it went down on the survey form as a female blue, it really helps to have a second opinion though. This is a shot with open wings, as you can see it's an old, worn individual. I guess the black spot wore off, which is odd as all the other female blues I've seen on site have really distinct black spots with white edges.

[bugboy]

That upper side is 100% Common Blue . Actually looks relatively fresh with only a few days were and tear to the fringe. The dull grey/brown ground colour and pale markings bordering the red lunules are enough to rule out Brown Argus.