In yesterday’s blog I was talking about the grey dagger caterpillar and how it used its bright yellow colours to deter predators from eating it. The predators have associated the colour yellow with poison. In the case of the grey dagger it is exploiting this fact as the caterpillar itself is not poisonous.
However one of our commonest moth – the day flying cinnabar (named as the reddish mineral cinnabar) has a caterpillar which is black and yellow/orange and is indeed poisonous.
Most people will have seen cinnabar moths caterpillars as they are common and feed on ragwort. Ragwort contains poisonous alkaloids which most other herbivores avoid – however the cinnabar is able to eat the ragwort without effect. It then incorporates the poison in its own body making it dangerous to predators. These caterpillars are therefore avoided and by association so are other species such as the grey dagger.