February 26, 2024

Brown Argus (Aricia agestis) or Common Blue?

Whilst taking some exciting macros of yesterdays Dragonfly species, I was briefly distracted by this butterfly.

I thought it was a female Common Blue (Polyommatus icarus), photographed it and got back to the Dragons, but when I got home and looked at the files on the big screen I started to wonder.

There’s more to ID-ing the Brown Argus than meets the eye. Mainly because the female Common Blue isn’t blue, she’s brown, mostly. Pretty sneaky eh? Of course, this cryptic colouration is not uncommon in the bird world, females often being dowdier than males, but it’s quite unusual among butterflies, except in the Lycanidea family, the Blues. To further confuse matters, the Brown Argus is also a Lycanid and so taxonomically at least, also a ‘Blue’.

Anyway, the crux of the ID relies on some fiddly little details on which I had intended to expound, but this would be a bit esoteric without some comparative shots of a female Common Blue. I don’t have any of those. I thought I did, but funnily enough, when I came to look at them in preparation for adding them to this post, I discovered that they too were of a female Brown Argus.

Instead I refer you to Steven Cheshire who has written a superb guide to identifying the two species, which can be downloaded from his excellent site www.britishbutterflies.co.uk. I’m indebted to him for this PDF as its helped me to add another insect to my species list and that’s always a good day, despite the fact that I’ve unwittingly already seen and photographed it!