Cinnabar moth

Have you found striped yellow and black caterpillars feeding on ragwort? These are the larvae of a cinnabar moth (Tyria jacobaeae), and their striped football jerseys are a danger signal.

Cinnabar moth caterpillars feed happily and almost exclusively on ragwort, which is poisonous to many, if not most, animals. The caterpillars absorb toxic alkaloids from the leaves they eat, but are not harmed by them. In fact, the alkaloids are protective: they make the caterpillar taste bitter to a predator.

The bitterness alone might not save an individual caterpillar. A hungry robin has to eat at least one to find out that it doesn’t taste good, but if the bird then goes elsewhere to look for something more palatable, the rest of the brood might be saved. However, if the whole brood is wearing black and yellow danger signals the bird could be warned away before he tries even one caterpillar, and then everybody is safe. It’s a clever strategy.

Cinnabar moths are classified as a UK BAP Priority Species (Research Only), which means that while they are not uncommon, their numbers are falling so rapidly that they are the subject of research. So if you have found striped caterpillars on ragwort, please look after them.