The large blue has a remarkable lifecycle, eggs are laid on the flower buds of wild thyme. The larvae burrow into the flower heads and when they are about 4mm long they drop to the ground and wait to be found by foraging red ants attracting them with sweet secretions from a “honey” gland. The ants place them in their brood chamber and the larvae feed on ant grubs to achieve most of their final body weight. Hibernating deep within the ant's nest the larvae pupate in early May within the nest and the newly emerging adults have to crawl up above ground before expanding their wings. 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.