Common Blue

I'd wanted her to be a Brown Argus (which we do get in this village, though I don't remember ever seeing one in the garden), and for a while I thought she was - largely because she was extremely skittish and wouldn't let me in close enough to pick up her markings by eye. But once I'd secured some photos and enlarged them, I could see that she was a Common Blue - still a fairly rare garden sighting, and certainly more interesting than most of my other subjects today. Having said which, I did photograph a Helophiluus hybridus down at the wildlife pond this afternoon - definitely a good garden tick, and number 53 on my hoverfly list for the year - but I had to photograph him from a distance, and the image wasn't as clear as this one.

Should you be wondering how I know this is a Common Blue, even though she didn't give me a single view of her overwing surfaces: the single spot on the forewing, close to the body (sometimes called the cell spot), is usually present in the Common Blue but always absent in the Brown Argus. Here it's cut in half by the edge of the hindwing, but it's very obviously there. There's another identification feature on the hindwing: the line of black spots ringed in white that lie just inside the orange markings form quite a clear arc, whereas in the Brown Argus they tend to be more irregular, with the two at the front edge of the wing usually separated from the rest and lying close together, in what's said to be a colon or a figure of eight mark - but all the underside markings in blue butterflies are subject to a degree of variation. The last thing I should say is that the Common Blue is bigger, with a wingspan of maybe 38mm to the Brown Argus' 30mm - but this isn't as helpful as one might like, with a single butterfly that's keeping its wings firmly folded.