Ragwort (Senecio jacobaea) is a common wild flower that is found throughout Europe, usually in dry, grassy places. Alternative names include St. James-wort, Ragweed, Stinking Nanny/Ninny/Willy, Staggerwort, Dog Standard, Cankerwort, Stammerwort and Mare's Fart. It has a long flowering period lasting from June to November. The leaves are pinnately lobed and the end lobe is blunt. The flower heads are 1.5-2.5 cm in size, and are borne in dense, flat-topped clusters.
Ragwort is the bane of people who keep horses. Although horses do not normally eat Ragwort, if the growth is particularly dense then some is eaten while grazing and causes irreversible cirrhosis of the liver. Sheep, in contrast, eat small quantities of the plant with relish and without apparent harm. The many names that include the word "stinking" (and Mare's Fart) arise because of the unpleasant smell of the leaves.
Ragwort is the food plant of the caterpillars of the Cinnabar Moth[?], Tyria jacobaeae. They adsorb toxins from the plant and becomes poisonous themselves, a fact advertised by the black and yellow warning colours. The red day-flying adult moth is also toxic or distasteful to many potential predators.
The moth is used as a control for ragwort in countries in which it has been introduced and become a problem, like New Zealand.