The black-veined white (Aporia crataegi) is a large, white butterfly whose caterpillars have a special overwintering strategy. They hibernate as young caterpillars (usually in the L2 stage) gregariously in a sturdy, self-spun silk nest, which they attach to the branches of their food plants (usually fruit trees or blackthorn). This nest protects the entire group of caterpillars from wind and weather. In spring, they leave the nest to continue their development.
[Photo: Reto Künzler, Bern]