Euonymus caterpillars are numerous in northeastern Illinois. This insect rarely occurs in Illinois south of Kankakee or west of Rockford. Its main host in Illinois is European euonymus, Euonymus europaea. It is listed as also attacking spreading euonymus, E. kiautschovicus, and winged euonymus, E. alatus; but I have not received reports of it feeding on those hosts. European euonymus is a slender, large shrub to small tree.
Euonymus caterpillar lives in a colonial silk tent that the caterpillars web between leaves. As the caterpillars grow, they expand the web to cover more leaves and branches. The caterpillars are whitish, with two rows of large black dots. When full grown, they are slightly over 3/4 inch long. The caterpillars pupate in the silt tent in June, forming rows of vertical silk cocoons.
Moths emerge and lay eggs on the twigs and branches and in bud axils in July. The slender moths have white wings peppered with small black spots. They are relatively small, with a wingspan of 1 inch. Within a few weeks, their eggs hatch into caterpillars, which crawl under their empty eggshells to spend the fall and winter. The caterpillars become active feeders and silk-tent constructors as the leaves emerge in the spring.
A wide range of insecticides are effective, but sprays must be applied with enough pressure to penetrate the silk webbing to reach the caterpillars. Bacillus thuringiensis kurstaki (Dipel, Thuricide) is the insecticide of choice, due to its specificity on caterpillars. (Phil Nixon and James Schuster)