Large Blue

• Latin name: Glaucopsyche arion
• Family group: Blues
• Countries: England
• Size: Small, Medium

Resident

Extinct (1979) and reintroduced since 1983.

This is the largest and rarest of our blue butterflies, distinguished by the unmistakable row of black spots on its upper forewing. The Large Blue is one of the most enigmatic butterflies, whose remarkable life cycle involves spending most of the year within the nests of red ants, where the larvae feed on ant grubs.

It has always been rare in Britain but declined rapidly during the twentieth century and became extinct in 1979. It has since been reintroduced successfully as part of an important habitat and species conservation programme.

Conservation status

• UK BAP status: Priority Species
• Butterfly Conservation priority: high
• European threat status: endangered
• Fully protected in Great Britain
• Bern Convention (Annexe IV) and EC Habitats and Species Directive (Annexe IV).

European/world range

Through Europe from central Spain to about 62B:N, and across Asia to China. Declining in most European countries and threatened throughout its global range.

Foodplants

Larvae initially feed on the flower-heads of Wild Thyme (Thymus polytrichus) but from their fourth instar they feed on ant grubs within the nests of the Myrmica red ants. Survival rates are highest within nests of Myrmica sabuleti and much poorer in those of M. scabrinodis. Eggs may also be laid on Wild Marjoram (Origanum vulgare) but this usually flowers too late to be used on most British sites.

Habitat

The Large Blue breeds in warm and arid (well-drained) unimproved grassland, predominantly acidic coastal grassland or limestone grassland. It also used to occur on calcareous clay soils, probably on dry outcrops or mounds