Most summers we have a small colony of cinnabar moths (Tyria jacobaeae) reproducing in the garden. The garish yellow-and-black caterpillars feed on species of ragwort and we leave a patch of common ragwort (Jacobaea vulgaris) to grow in the lawn. The caterpillars eat for a few weeks, virtually destroy the ragwort, and in the process accumulate alkaloids from the host plant into their bodies. This renders them toxic in much the same way as monarch butterflies accumulate toxins from their Asclepias food plants – see my recent post about the Monarchs and Milkweeds workshop. Hence the stripes to warn birds of their unpalatability.
Ragwort is a much-maligned plant, hated by those with horses and livestock, and subject to a largely hysterical campaign of eradication – see here for example. However John Clare clearly appreciated its virtues in a poem dedicated to the plant:
Ragwort, thou humble flower with tattered leaves
I love to see thee come & litter gold,
What time the summer binds her russet sheaves;
Decking rude spots in beauties manifold,
That without thee were dreary to behold.
Once they have fed their fill, the caterpillars dig themselves into the soil to spend twelve months or so underground as pupae, before emerging as gorgeous adult moths, advertising their toxicity with a different colour scheme.
The adults live for a few weeks at most, during which time they feed on nectar, mate, lay eggs and die. This (unposed) photograph that I snapped on my phone in the garden yesterday just about sums it up: an exhausted mother has laid her last batch of eggs then died, while a nearby young caterpillar munches away on the ragwort. And so the generations pass.