Ants are among the most successful of living things. Their nests are well-defended fortresses, coordinated through complex communication systems involving touch and chemical signals. These strongholds are stocked with food and secure from the outside world, so they make a tempting prospect for any burglars that manage to break in.

One species of butterfly – the mountain alcon blue (Maculinea rebeli) – is just one such master felon. Somehow, it manipulates the workers into carrying it inside the nest, feeding it and caring for it. The caterpillar does so little for itself that it packs on 98% of its eventual adult weight in the company of ants. How does it do it?

Partly, the caterpillar secretes chemicals that imitate those found