In the male, wings are dark purple, with black outer margins. The female's wings are dark brown with a purplish blue area on the forewings. A butterfly which is easily overlooked, as it tends to fly around the upper branches of oaks (and alders). So if you go looking for this one, take your binoculars!
Wingspan 33 - 40mm (male), 31 - 38mm (female).
Single brood, adults appearing in mid-July. Ova laid in July - August, and although larvae develop within three weeks, they overwinter without hatching until April. Larval stage lasts between six and seven weeks. Pupal stage lasts four weeks.
July to September.
This species was added to the Highland list in 2004. It was discovered in oak woods in Morvern.