Papilio polyxenes asterius This insect pest is the larva of the black swallowtail butterfly. It is also called the celeryworm. As its names suggest, it feeds on parsley and celery, as well as on dill and parsnips. Although seldom a serious pest, these worms may strip plants of foliage. In the North, they spend the winter in tan cocoons hanging from host plants. The adult butterfly overwinters in the South. The butterfly has black wings spotted with yellow, orange, and blue dots and a wingspan of 3 to 4 inches. The worms that hatch from eggs laid on the leaves feed on the foliage for several weeks, pupate in suspended cocoons, and emerge as adults to repeat the cycle. Two to four generations occur per year.