Northwest Florida doesn't have the highest concentration of the common bagworm, Thyridoptgeryx ephemeraeformis, but most plants bagworms feed on can be found here.
Common host trees include red cedar, live oak, maple, elm and pine. Other susceptible shrubs include Indian hawthorn, juniper, arborvitae, ligustrum and viburnum.
Finding a host
Bagworms overwinter as a clutch of 500-1,000 eggs wrapped in an infested plant's leaves. Larvae hatch in late spring as tiny caterpillars that disperse to surrounding plants, spinning a silken thread and “ballooning” on the wind.
Once established on a host plant, the young bagworms feed and construct a bag using pieces of twigs, leaves and silk.
Then, the female bagworm's head and thorax emerge from the foliage bag. She continually feeds on the plant, leaving it severely defoliated. As few as four bagworm larvae can cause a 4-foot arborvitae to be so damaged that it can’t ever grow enough foliage to return to normal appearance.
The caterpillars feed steadily for four to 16 weeks. Once the larva has consumed enough food, it attaches its bag securely with a thick silken strand to its host plant or nearby structure.
The bagworm seals the bag's posterior end, molts and begins pupation. The bagworm’s seven- to 10-day metamorphosis results in a moth. However, the adult female’s wings and appendages are reduced to mouthparts, legs and small eyes. She remains in a caterpillar-like state a couple of weeks and releases a pheromone that attracts the male.
The male bagworm emerges as a free-flying, lacey, black moth that lives one or two days — just enough time to mate with the female in her bag. Once mated, the female dies, mummifying around her eggs.
Controlling the population
Bagworm populations can reappear in the same areas year after year. Mechanical methods and biological insecticides are the most effective practices to control bagworms.
Handpick them from late fall to early spring and place them in a bucket of soapy water or a sealed bag to prevent new larvae from dispersing. Applying Bacillus thuringiensis, or Bt, to the foliage is an effective means of control when applied to new spring growth.
This bacteria stops all caterpillars' feeding, so be cautious about where it is used. Many desirable butterfly larvae can be harmed if the product lands on other larval plants.
Sheila Dunning is an agent at the University of Florida's Extension office in Crestview.