In pictures taken in early July, cinnabar moth caterpillars crowd on their preferred food plant, a ragwort.
Ragworts have evolved poisons to discourage insects and other animals from eating them. Cinnabar moths in turn evolved to be immune to these poisons, to be able to store them in their own bodies to discourage their predators. That’s handy when their adult form is quite large for a moth, day flying, brightly coloured and generally quite conspicuous.
The moth advertises it’s bad to eat by its warning colouration: black and yellow stripes in the caterpillar, black and scarlet in the adult.