Bagworms (Thyridopteryx ephemeraeformis) are destructive insects that attack many deciduous and evergreen trees and shrubs. Young bagworm caterpillars feed on needles and leaves and a large infestation can lead to almost complete defoliation of trees. Some of the more common evergreen host plants include arborvitae (Thuja), fir (Abies), hemlock (Tsuga), juniper (Juniperus), pine (Pinus) and spruce (Picea). Deciduous host plants include black locust (Robinia pseudoacacia), honeylocust (Gleditsia triacanthos), sweetgum (Liquidambar styraciflua) and sycamore (Platanus occidentalis).
Bagworms can be recognized by the characteristic case or "bag" that they construct around themselves. The bag is made from silk and plant material from the plants they are feeding on.
Eggs of bagworms hatch in late May and early June from bags that were constructed the previous season. The larvae (caterpillars) construct a bag around their hind parts after hatching and carry it around as they feed on needles and leaves throughout the summer.
In August, the mature larvae attach their bags to a branch (looking a lot like small pine cones) where they stay for about 4 weeks in a pupa stage.
Males emerge from the cases in September or October in search of females. The adult females remain in their bag, releasing a pheromone to attract the males. They mate and lay their eggs without ever leaving the bag.
Female bagworms can lay up to 1,000 eggs which overwinter in the bags and hatch out the following May.
Bonide products can be found in most full service garden centers.