December 12, 2017

Common Blue (Polyommatus icarus)

Kind of a follow up to yesterday’s species and I’d obviously have preferred a female Common Blue for comparative purposes, but beggars can’t be choosers.

P. icarus is very common throughout almost all habitats in the UK and as such is pretty familiar to even the most casual urban butterfly spotter. Along with Large and Small Whites, Small Tortoiseshells and the odd Speckled Wood, they were a staple species for my earliest forays into lepidoptery.

This male is nectaring on Bird’s-foot-trefoil (Lotus corniculatus), who’s leaves are also the main food plant for this species’ larvae or caterpillars. This is a nice illustration of the inter-relationship between insect and plant because the trefoil itself benefits by being pollinated as the butterflies feed.

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!

Gatekeeper (Pyronia tithonus)

A common butterfly almost anywhere shrubs meet rough grassland. Superficially pretty similar to the related Meadow Brown (Maniola jurtina) but a little smaller, with a larger amount of orange, particularly on the hindwings and having two white pupils instead of one in the forewing eyespots. This individual is a female, the males have a very obvious dark patch of scent scales on their forewing.

The larvae feed on grass species like Bents, Fescues, Meadow Grasses and Common Couch. The adults feed on the nectar from a wide variety of plants including Privet, and Thistles and Brambles so their ubiquity, to some extent ,must be related to their fairly catholic tastes.

The flight season is relatively short with adults having only one generation and being in flight from the second half of July up until the end of August. This is significantly less than M. jurtina which also only has one generation a year, but has a much greater flight period from mid June to late September.