This strikingly coloured moth is the Cinnabar moth. The plant it is on is common ragwort (Senecio jacobaea – which is looking a bit tatty as it has recently been mowed). Ragwort is the principal food plant for the caterpillars of the Cinnabar moth. The caterpillars are equally striking, but they are striped black and yellow.
In the UK, there are few plants that excite such heated debate as ragwort does. Sadly, the debate is generally more heated than considered.
Ragwort, like very many plants, does contains naturally occurring “toxins”: specifically, pyrrolizidine alkaloids. These alkaloids are produced by vast numbers of plants. The alkaloids make the plants taste bitter and unpalatable, thus deterring herbivores from eating them.
The risk from ragwort comes when it is dried and mixed in with a hay crop – then animals are less able to detect the bitterness and also unable to sort out the different herbage and forage and consequently more likely to ingest ragwort (or any other undesirable plants).
So, ragwort does have some risks, but it also has lots of benefits, including being a food plant for dozens of insects, including several endangered species. It isn’t a plant that warrants a knee-jerk panic reaction, but a considered assessment of its potential risk and benefits in any given situation.
In 2010, the Welsh Government published new guidance on ragwort control. This Code of Practice presents a surprisingly balanced analysis of the ragwort situation, as well as guidance on control strategies as and when appropriate. It is freely available for download from the Welsh Government website.