This large gathering of Escher's blues was found on a roadside in southern France in 2015. There may have been up to 80 in total. They seemed to be focussed on feeding and were not unduly bothered by our presence. Although it was a quiet country road there were occasional cars and it was heartbreaking to witness some of the swarm being flattened by a passing vehicle. Even this didn't seem to put them off.
The butterflies with greyish underwings are males; there are a few females - these are brown underneath. Other species often mingle with the crowd but can be difficult to identify.

An aberrant butterfly shows a variation (aberration) in its usual wing pattern, thought to occur because of extreme conditions during the butterfly's development e.g. very cold temperatures or sudden environmental changes. Aberrations are rare but have been recorded for many species.
Here, the aberrant Escher's blue has dark strong smears down its wings and can be seen near the top left corner of the picture.
Further images of it appear below.