A very common plant of waste ground and pastures. It is poisonous to livestock, especially horses, so working parties of volunteers often organise a "Ragwort pull" before the grass is cut for hay.
The yellow and black-striped caterpillars of the Cinnabar Moth feed on Ragwort, accumulating the toxins to protect themselves against birds. These caterpillars can strip the whole plant, hence are often left to save effort during the Ragwort pull.

Cinnabar moth caterpillar on ragwort