Bagworms have been identified on evergreen trees throughout Roselle for the past two years. Bagworms spread slowly because the female is unable to fly, but they can be blown by the wind or crawl to other host plants. Landscapers may unintentionally transport bagworms in the process of pruning and moving infested plant material.
Bagworms can be identified by spindleshaped bags one or two inches long that hang from trees and shrubs. The bags which look like cones contain eggs that produce a brood of caterpillars during the latter part of June. Newly hatched caterpillars may easily be overlooked. On leaving the mother bag, the caterpillars feed on nearby foliage and construct a new bag with silken threads and bits of foliage taken from the host plants. Bagworms feed on foliage of evergreens as well as on a wide variety of deciduous trees and shrubs. These plants may be partly or almost completely defoliated. Defoliation of deciduous trees generally does not cause them to die, but a defoliated evergreen is likely to die.
Severe infestations may require treatment. It is important to spray while the caterpillars are small, soon after all eggs have hatched in the latter part of June; it may be necessary to repeat the spraying if rain follows soon after the treatment. When practical, the bagworms can be removed and destroyed. Simply pick the bagworms bag off the plant and dispose of them. Be sure to cut the attachment silk band so that the branch will not be girdled in the future.
Click here for photos of bagworms. For more information, contact Village Forester Mike Schulz at (630) 671-2368.
(Source: University of Illinois Entomology fact sheet)