Cinnabar Moth caterpillars easy to spot on ragwort
Cinnabar Moth caterpillars are big and fat at this time of year and are easily spotted as they are almost exclusively found on Ragwort - an Buachalán Buí - and have colourfully hooped bodies reminiscent of the black and amber of Kilkenny GAA stockings.
The species is common and widespread and is found all over Ireland especially on mature sand dunes so, on a trip to the seaside, the caterpillars are frequently seen in open grassy places near the coast.
Mother Cinnabar Moth laid a cluster of eggs on the underside of a Ragwort leaf last June. When the caterpillars emerged from the eggs they were small in size and yellow in colour. As they gorged themselves on all parts of the plant they grow bigger and turned a bright orange decorated with very dark grey, almost black, hoops.
Ragwort is a poisonous plant. Amazingly, as they feed the caterpillars are able to extract the poisons and store them in their bodies to make themselves unpalatable to birds that might eat them.
While the black and amber pattern is interpreted as warning coloration to ward off predators, the Cuckoo is said to seek out Cinnabar Moth caterpillars and to eat them with impunity.
At this time of year many families of the voracious caterpillars have stripped their food plant bare. Some leave and go walkabout searching for another nearby Ragwort to eat. Others turn cannibalistic and devour their siblings; the strong survive by eating the weak.
Cinnabar is both a colour and a mineral. The red pigment is made from the mineral mercury sulphide, an ore of mercury, and the colour occupies a place on the artist's palette close to scarlet and vermillion. The adult moth is very dark grey, almost black, in colour and is named after the colour of its red hind wing. Its forewing has two large spots of cinnabar on its outer edge and a bold, broad band of the same colour along its front margin.
While mainly nocturnal, the moths may commonly be seen flying on sunny days and may be mistaken for butterflies due to their colourful bodies.
Come September, the Cinnabar Moth caterpillars will be fully mature. They will descend to the ground, turn into pupae and overwinter in that form awaiting the arrival of next spring. Next May, the pupae will burst open, the adult moths emerge and fly off to find partners, mate, lay eggs on Ragworts and start the cycle all over again.