Often there may be 50-100 feeding in a group. Young larvae eat the outer tissue of the needles while older larvae eat the entire needle thus causing the defoliation. The insects are most active during late summer or fall. No tree mortality resulting directly from needle loss has been reported. However severe defoliation causes weakening of trees and susceptibility to attack by bark beetles.
Adult males have feathery antennae.
Larvae, depending on the species may be bright yellow with black spots or olive green to nearly black with dark stripes along the sides. Some species are solid green with darker spots. Full grown larvae are about 1-inch long. On the small yard pine trees and Christmas trees, hand removing the larvae is an effective control since they feed in groups and are easily accessible. Heavy population on larger tress can be controlled with Orthene or dursban.