Although reputed to be poisonous to cattle, you may well find cows grazing without any ill effects in field where Cowbane grows in the damp or marshy places. The poisonous element is called Cicuotoxin and is contained in the yellowy resinous sap but seems to be most concentrated in the roots rather than the stem and leaves which cattle would perhaps first graze upon. But I doubt the cattle would normally touch it just as horses in fields of Cheshire frequently graze all late summer in fields full of Ragwort (Senecio jacobaea).

C. virosa has a strange distribution with the highest concentration south of Cheshire and in Shropshire. Otherwise the main concentration is in the middle and in northern Ireland with just odd records here and there in the rest of the British Isles.

Marshy land near Ruthven Barracks, Scotland, 26th July 2009

Added on September 25th 2009, updated 14th March 2010