Young larvae feed in groups on the undersides of the leaves. After a few days of aggregated feeding they separate and feed alone. They typically skeletonize the leaves and when the damaged leaf dries, it tatters in the wind, breaking off and leaving only the main vein. Adults also feed on the leaves. First generation damage can be serious on ornamental willows but is not of much concern on wild trees.
Later generations seem to cause very little damage.
The adults overwinter under bark, litter, or debris under or near trees. They begin to emerge in late March or early April and egg laying is underway by mid-April. May. The larvae have a row of glands down each side of the body that produce a foul-smelling milky fluid. When a larva is disturbed, it emits a droplet of this fluid from each gland. Predators rarely attack these larvae, and it is assumed that they are repelled by the odor.