Bagworms are a yearly pest in our area and can cause considerable damage. Most homeowners typically dont get too concerned about bag-worm control until they see large bags present on plants. By then it is too late and the damage is already done! I actually found newly hatched bagworms on my Bald Cypress trees over the weekend.
Bagworms overwinter as eggs deposited in the female bags. From mid-May through mid-June, larvae hatch from the eggs and exit from the bottom opening of the old bag. Larvae begin constructing their miniature silk-lined bags immediately. Only after the bags have been completed do the larvae begin actual feeding activities. And as the larvae grow, so do their bags. By mid-to late August when feeding activities are complete, larvae firmly anchor their bags to the twigs and branches on which they were feeding.
Bagworms are most commonly found on eastern red cedar and junipers. However, bag-worms can attack arborvitae, spruce and pine. Broadleaf trees, shrubs and ornamentals can also serve as a host to bagworms. After bag-worms have defoliated a host plant, they are capable of migrating in search of additional food sources. They may attack the same species from which they came or a completely different species.