The restoration of the large blue butterfly to the UK

Summary

The large blue butterfly (Maculinea arion), an IUCN-flagship invertebrate whose larvae parasitize Myrmica sabuleti ant colonies for up to two years, went extinct in the UK in 1979 despite five decades of earlier conservation efforts, which had misidentified the cause of decline. Research by the Nature Conservancy and Institute of Terrestrial Ecology in the 1970s revealed too late to save the last colony that the butterfly depends specifically on M. sabuleti, which had disappeared from most sites as grazing declined and turf grew too tall for the thermophilous ant; Dartmoor trials then showed regulated spring and autumn grazing plus scrub clearance could rapidly restore the ant. After physiological testing identified Sweden's Oland population as climatically compatible, an initial 1982 trial release of pre-adoption larvae succeeded, followed by transfers of 245 and 581 larvae in 1984 and 1991 to three UK sites, one of which failed, and further smaller introductions of 200-300 larvae to additional sites through 2000, sourced from the growing UK colonies themselves. By 2011, nearly 100 sites were under grassland management aimed at supporting the species, about 60 meeting minimum habitat criteria, and colonies had been restored or spread naturally to 38 sites, including three among the largest known large blue populations worldwide, two of which have persisted unaided for 20 generations. Major difficulties included uncertain long-term funding and, in one region, institutional resistance to science-based habitat restoration. The project rates itself Highly Successful, crediting close, decades-long collaboration between scientists, landowners and conservation bodies coordinated by a dedicated project leader.