Pretty, but dangerous!

These yellow flowers belong to Jacobaea vulgaris,  a very common wild flower in the daisy family that is native to northern Eurasia. Its common names include ragwort, common ragwort, stinking willie, tansy ragwort, benweed, St. James-wort, stinking nanny/ninny/willy, staggerwort, dog standard, cankerwort and stammerwort. 


Ragwort contains copious pyrrolizidine alkaloids that make it poisonous to many animals including horses and cattle. Despite the presence of these poisonous alkaloids,  the leaves are the food of choice for the caterpillars of the cinnabar moth. Such a diet means that  the caterpillars themselves become poisonous and their striking colouration is a warning to birds to leave them well alone. 
The moths are very scarce this year and I have searched high and low for their caterpillars.  These are the only one that I have discovered.