Establish Natural Defenses
Bagworms appear in May and June in the North and a bit earlier in the South. While they are still moving around dragging their partially formed bags with them as they feed on tree and shrub foliage they are vulnerable to birds. If you feed birds and put up birdhouses for them in the yard they are likely to be in the area at this time. patrolling for protein for themselves and their nestlings. Predator birds can make a big dent in the bagworm population.
Keep Trees and Shrubs Vigorous
Unless the underlying stress that made your trees and shrubs vulnerable to bagworm attack is identified and corrected, they may return next year. Give some thought to the situation that the affected tree or shrub is in. Make an effort to improve its vigor by watering it during dry periods over the summer and feeding it in the fall. Prune any broken or injured limbs cleanly and carefully. Mulch it to discourage weeds, hold soil moisture and improve the soil under it. Make sure it is still getting enough light as the surrounding trees age and block the sun a bit more.
Attract Beneficial Insects to the Yard
Strengthen nature’s first line of defense by planting a diversity of plants that will host birds and insects that prey on bagworms. If there is a healthy population of ants and spiders working in the trees when the bagworm moth lays her eggs in the fall, then they will eat many of those eggs before they have a chance to hatch. Also, the tiny ichneumon fly parasitizes bagworm larvae. Grow a variety of plants--trees, shrubs, lawn grasses, flowers, vines and groundcovers to attract and harbor a variety of beneficial insects allies
Feed Birds Year Round
Birds that eat bagworms include:
In the wintertime, nuthatches, chickadees, and titmice work up and down the bark of trees looking for insect eggs to eat--including those of the bagworm. Set up a feeding station and keep it stocked with a quality birdseed mix and suet to attract these birds to your yard. Put up houses to encourage them to set up housekeeping and raise their young. Then the birds will also feed on the bagworm caterpillars in the spring. The more birds you attract to your yard over the years, the more protection you will have from bagworms.