Growth and development in the ant nest Once inside the ant nest, the caterpillars are fed by the ants much as if they were their own larvae. Worker ants regurgitate liquid food that the caterpillars drink. The ants seem to prefer feeding caterpillars to feeding their own larvae, so that fewer ant larvae can develop. In the laboratory the caterpillars will also eat ant larvae directly, and this probably also happens in nature (some other large blue butterflies live entirely by eating ant brood when they are inside the ant nest). Although caterpillars will be adopted by any Myrmica ant species that finds them, they are only seem able to survive in the nests of one or two species of ant. The Alcon blue is unusual among the large blue butterflies in that the species of ant in the nests of which it can survive is different in different parts of Europe. At the moment we are carrying out research at the Universities of Copenhagen and Aarhus into why this should be.

If caterpillars are adopted into a nest of the right species of ant they will grow rapidly, increasing in weight about 100 times in their first month in the nest. They will stay in the nest throughout the autumn, winter and spring, and will turn into pupae in the early summer.