This fine insect is Europe’s second-largest blue butterfly, being just a millimetre or two smaller than the elusive Iolas Blue. Whilst it has never occurred in Ireland it was once found in southern Britain until the late 20th century. It has since been reintroduced and survives in a few areas in the southwest of England. Unusually for butterflies the larva are partly insectivorous as they feed on Thyme or Marjoram flowers in their early instars before falling to the ground, emitting an ant pheromone before being brought by the worker ants to their nest  where they will feed on ant larva before pupating. I failed to find it in Romania but I found one worn specimen in Gavarnie in the middle of July, right at the end of the flight period. It is listed as Endangered in Europe.

Distribution: Most of Europe. Absent from most of the UK, S Iberia, S Greece, S Italy, N Fennoscandia and the Mediterranean islands (except Corsica).

Flight Period: Late May-July in 1 brood, peaking in June.

Habitat: Dry meadows, dry scrub, sunny woodland clearings, grassland up to 2000m, usually on calcareous substrates.

Foodplants: Breckland Thyme (Thymus serpyllum) and Creeping Thyme (Thymus drucei) in cooler areas, Marjoram (Origanum majorana) in warmer localities.

Nectar Sources: Thymes (Thymus), Self-heal (Prunella vulgaris), clovers (Trifolium).

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