Peucedanum palustre is an almost glabrous biennial plant in the family Apiaceae. It is so called in English because of the thin, foetid, milky latex found in its young parts and is native to most of Europe, extending eastwards to Central Asia. Another English common name for the plant is marsh hog’s fennel. Milk–parsley is the main food of swallowtail butterfly caterpillars. Both the caterpillar and the adult butterfly warn off birds and other predators with their bright colours and bad taste, which is a product of compounds in the vegetation they eat which is stored in their bodies.