In fact, its leaves contain an alkaloid poison. The poison also stays in plants that have been dried with hay. In this state it can be eaten by farm stock and will destroy their livers over a period of months.
'Ragwort' refers to the ragged leaves. The Scots call this plant 'stinking Billy' because it smells unpleasant when bruised. 'Billy' was William, Duke of Cumberland, who was victorious at the Battle of Culloden in 1746 and vicious in his reprisals against the Jacobites. Sweet Williams (Dianthus barbatus) are also known as 'stinking Billy'.
The butterfly is a Wall Brown (Lasiommata megera) I think but feel free to correct me if you know better. There is also a bee on the ragwort.