Species Profile
Red List; nationally scarce and restricted to managed conservation sites; extinct across most of former range.
- Lifespan
- 2–4 weeks as an adult butterfly; up to 2 years as a larva within ant colonies
- Size & Weight
- Wingspan 32–36 mm; weighs approximately 0.3–0.5 g
- Habitat
- Calcareous grasslands and limestone hills with abundant wild thyme and specific Myrmica ant colonies.
- UK Distribution
- Restricted to a few sites in south-west England, primarily Devon and Cornwall; reintroduced populations are resident (non-migratory) and heavily dependent on conservation management.
- Diet
- Adults feed on nectar from wildflowers, particularly bird's-foot trefoil and other legumes; larvae feed on thyme flower buds.
- Predators
- Birds, spiders, and parasitoid wasps; parasitic flies and flies of the genus Phryxe also attack larvae.
- Mating Season
- June to July
- Breeding
- Females lay single eggs on wild thyme plants; larvae are adopted and reared by Myrmica ant colonies (usually M. sabuleti or M. scabrinodis); one generation per year.
- Behaviour
- Adults exhibit strong site fidelity and rarely disperse far from breeding sites. Larvae are social parasites of Myrmica ants, secreting chemicals that mimic ant pheromones to gain entry and care within ant nests. Males perch on vegetation to watch for females.
Did You Know?- •The Large Blue was extinct in Britain by 1979 but has been successfully reintroduced through intensive conservation breeding and reintroduction programmes.
- •Larvae are obligate social parasites that feed on ant larvae within the colony, exploiting the ants' own brood-care behaviour.
- •Adult emergence is precisely timed to coincide with the activity patterns of specific Myrmica ant species; timing mismatch with ants can cause population crashes.
- •The species requires a mosaic of bare ground, thyme, and ant colonies, making it extremely sensitive to habitat management and climate change.
- •Genetic monitoring has been crucial to reintroduction success, with individuals sourced from Swedish populations where the species remains common.
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