Dogfennel is a perennial herbaceous plant, resembling a small pine tree in appearance. Its feathery leaves are rich in pyrrolizidine alkaloids and are greatly adored by male Danaid butterflies, as after intaking the leaf sap, they are able to produce pheromones to attract the opposite sex. Withered Dogfennel emits an even more intense odour, drawing large numbers of Danaid butterflies to flutter and linger among the plants, displaying a breathtaking spectacle.