Control Bagworms in Late May and Early June

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A bagworm nest hanging from an evergreen tree.Have you noticed cone-shaped bags hanging from your conifer trees? Now is the time to control bagworms. Bagworms are a common landscape pest that feeds on many of the most common ornamental plant species. They are especially problematic for conifers such as Leyland cypress, arborvitae, and cedars.

Female bagworms lay 500-1,000 eggs in their bag before they die in the fall. The eggs overwinter and hatch in May and June. The newly hatched larvae crawl to foliage to feed or spin down on silken threads that are blown about in the wind. This behavior is called ‘ballooning’ and helps bagworms get to new plants. Upon reaching a suitable host, the worm spins a tiny bag of silk and plant debris that looks like an upside-down ice cream cone. As the caterpillar grows the bag grows also and more host plant material is added to the outside for camouflage. In addition, the larger bags hang down from branches like pine cones rather than sticking up. In August the caterpillars mature and molt into the pupal stage. The bag is attached by a sturdy silk band, which the bagworms usually wrap around a twig. During August and September, adult bagworms emerge as moths from the pupal case. Females are flightless and never leave the bag so male moths emerge from their bags in search of females to mate with. Mating occurs through the bag. After mating, females lay their eggs inside the pupal cast skins and die.

Bagworms can cause severe damage to landscape plants by defoliating branches that alter plant shape and foliage density. The decision of when and how to control bagworms will depend on the size of the populations and on plant location, value, and purpose.

Late May or early June is a perfect time to spray for bagworms as then the caterpillars are tiny and very susceptible to pesticides. At that time, use a pyrethroid such as permethrin or bifenthrin because pyrethroids have a longer residual life than most other insecticides. These pesticides are readily available at most garden centers and big box stores.

If the bagworms are first noticed in late summer, it is too late to do anything but physically remove the bags. By then they have already mated and females have already laid eggs inside their bags for next year’s generation. It’s best to use a very sharp knife or utility razor to cut the silk band that bagworms wrap around and around the twig just before they pupate inside.

For more information check out our Bagworms in Ornamental Landscapes publication.

If you have any specific questions about bagworms, contact your local County Extension Center. For Camden County residents contact Camden County Agriculture Agent Austin Brown at (252) 331-7630 or