Eating its way along a toadflax plant, also called butter-and-eggs (Linaria vulgaris). Both the plant and the caterpillar are from Europe. The caterpillar was introduced in Canada in the 1960's to control toadflax. Whether it is working or not, seems to be up for debate, but I know that I do not see as many plants as I used to. At the Fletcher garden there are very few at present.