Peacock caterpillars

The peacock caterpillars will be growing fast at this time of year.

The female butterfly mates in the spring and lays her eggs, several hundred of them, under the topmost leaves of new nettles growing vigorously somewhere sunny. About two weeks later the eggs hatch into black spiky caterpillars with white spots. Like small tortoiseshell caterpillars, which they resemble at this stage, they stay together and spin a web around the top of the nettle to protect themselves from predators and adverse weather.

They eat; this is their job. The caterpillar must eat enough to reach sufficient size (4.2cm) to pupate before the summer is over. A caterpillar’s skin doesn’t grow with it and has to be moulted when it gets too tight; caterpillars will moult four or five times before they pupate and the stages between the moults are called instars. With each instar, the peacock caterpillars become more independent and move further away from the group.

In July and August, they pupate. They leave the nettle bed for thicker undergrowth or trees and attach themselves to a leaf or a twig, hanging with their head down; their skin splits one last time and exposes the chrysalis inside. The chrysalis can be a range of greenish colours depending on its position and has a reflective, almost metallic, quality that makes it very difficult to see.

The new adult hatches in 12 – 14 days. It feeds on nectar for the remainder of the summer and hibernates from October until the following spring.