August 2011 - Cinnabar Moth

Taken by Lin, UEA 17th June 2011

If you are out walking in our local fields where ragwort is growing in the summer months you are likely to see cinnabar caterpillars. These photos were taken while I was out walking at the University of East Anglia. As you can see these caterpillars are very striking being striped jet black and yellow/orange. They feed voraciously, in numbers, and can decimate large areas of the food plant, leaving just the stems. Although ragwort is their favourite food plant, they will also feed on groundsel and coltsfoot. Cinnabar moths have been introduced in the past into New Zealand, Australia and North America in an attempt to control ragwort which is poisonous to livestock. There have been reports from the United States that ragwort has been effectively controlled when the cinnabar moth has been used as a bio-control agent in conjunction with the ragwort flea beetle.

Here in Norfolk there are reports from the Norfolk Wildlife Trust that numbers of cinnabar moths have declined by 83% in the last 35 years, the possible reason being the eradication of ragwort in livestock fields. Far from being poisonous to the caterpillars they are able to store the alkaloid poison in their bodies which is then retained for the whole life cycle of the insect through to the adult moth. These alkaloids give the caterpillars and moths a very unpleasant taste and birds soon learn to recognise both caterpillars and moths by their striking appearance and leave them well alone. Once the food plant source starts to dwindle, cases of cannibalism have been reported amongst the caterpillars. 

  Taken  by Lin,  UEA 17th June 2011

The caterpillars pupate in thin silken cocoons which lie just in the soil or amongst surface litter near the food plant. These cocoons over winter, the nectar drinking moths emerging in May. Like the caterpillars, these moths are also strikingly coloured, with bright red spots and stripes on their upper charcoal grey/black wings and hind wings of bright red edged with charcoal. They have a wing span of about 1.5 inches. The moths can be seen flying sluggishly in day light during the summer, but are primarily night fliers. Females lay up to 300 shiny yellow eggs, usually in clusters of 30 to 60.

The cinnabar moth is named after the bright red mineral cinnabar.

Taken by Lin, UEA 2nd July 2012


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