Large Blue

This is the largest and rarest of our blue butterflies, distinguished by the unmistakable row of black spots on its upper forewing. Undersides are pale brown with black spots. 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.

The Large Blue has always been rare in Britain and became extinct in 1979, but it has been reintroduced from continental Europe as part of a long-term and highly successful conservation project.

The Large Blue is declining throughout its world range and is endangered globally.

Size and Family

• Family: Blues
• Size: Small/Medium
• Wing Span Range (male to female): 38-44mm

Conservation Status

• Section 41 species of principal importance under the NERC Act in England
• GB Red List (2022): Near Threatened    
• Butterfly Conservation priority: High                         
• European status: Endangered                                 
• Fully protected In Great Britain   

Caterpillar Foodplant

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 be laid on Wild Marjoram (Origanum vulgare) but this usually flowers too late to be used on most British sites.

Lifecycle

Distribution

• Countries: England
• Very rare in south-western England and only found where it has been painstakingly reintroduced by conservation organisations.
• Abundance trend: 1883% (1983-2019)
• Distribution trend: not assessed

Habitat

Warm and well-drained unimproved grasslands, usually acidic coastal grassland or limestone grassland.