Some caterpillers just don't want to grow up

For many years, ecologists from the Centre of Environment and Hydrology (CEH) have investigated the ecology of Maculinea rebeli, a Lycaenid butterfly whose caterpillars live as parasites inside colonies of Myrmica ants, where they feed on regurgitations from the nurse ants. One of the peculiar features of this species' ecology is that only about 25% of the caterpillars complete development within one year. The rest are inactive in the first season and mature only after two years.