Brown Argus
The diagnostic feature for separating Brown Argus from female Common Blue, is two spots on top of one another at the top edge of the Brown Argus hindwing, creating a figure of 8 like this: www.flickr.com/photos/timmelling/5990925447/in/photolist But this Brown Argus that I photographed in my friend's Rutland garden, lacks this feature and so superficially resembles a Common Blue like this: www.flickr.com/photos/timmelling/5799969922/in/photolist The spot in question appears to be slightly comma-shaped so maybe the two spots have merged. To add to the confusion the Brown Argus was nectaring on Bird's-foot Trefoil, which is the larval foodplant of Common Blue. An additional identification feature is the marginal orange lunules on the forewing. In Common Blue they usually peter out towards the tip, whereas on Brown Argus they are solidly orange right to the tip, as they are here.
Brown Argus
The diagnostic feature for separating Brown Argus from female Common Blue, is two spots on top of one another at the top edge of the Brown Argus hindwing, creating a figure of 8 like this: www.flickr.com/photos/timmelling/5990925447/in/photolist But this Brown Argus that I photographed in my friend's Rutland garden, lacks this feature and so superficially resembles a Common Blue like this: www.flickr.com/photos/timmelling/5799969922/in/photolist The spot in question appears to be slightly comma-shaped so maybe the two spots have merged. To add to the confusion the Brown Argus was nectaring on Bird's-foot Trefoil, which is the larval foodplant of Common Blue. An additional identification feature is the marginal orange lunules on the forewing. In Common Blue they usually peter out towards the tip, whereas on Brown Argus they are solidly orange right to the tip, as they are here.