Invertebrates
Large Blue
Phengaris arion · also called large blue butterfly
Beneath the surface of a thyme-covered hillside, a large blue caterpillar lies among the grubs in a red-ant nest, fed by the very ants it has fooled.
Overview
The large blue, Phengaris arion, is an Endangered butterfly of flowery grassland from western Europe to central Asia. Its extraordinary life cycle, in which the caterpillar is adopted by ants and eats their grubs, and its reintroduction to Britain make it one of the most famous butterflies in conservation.
A cuckoo among the ants
The large blue’s dependence on both thyme and one species of red ant shows how closely some butterflies are tied to the other animals around them.
Status
Endangered, with a decreasing population.
Large Blue: common questions
How does the large blue caterpillar trick ants?
It gives off a scent that makes red ants carry it into their nest, where it feeds on the ants' grubs.
Was the large blue extinct in Britain?
Yes, it died out in Britain in 1979 and was reintroduced from Sweden in the 1980s.
Why does the large blue need conservation management?
It depends on the right species of red ant and on grassland grazed to the right height, so management keeps both in good condition.
Where is the large blue found?
It lives in flowery grassland from western Europe to central Asia, but is now rare in many countries.