What are Bagworms?
Bagworms are highly invasive insect species that, in large numbers, have the ability to take down large Eastern Red Cedar trees in a short amount of time. Unlike traditional worms, they hatch in late spring as tiny caterpillars. In their caterpillar state, they weave a thin silk thread that carries them with the wind to another host plant. During this time, they generally attach and feed off of Juniper, Cypress, and Arborvitae trees, while also constructing their silk bag portable home, which looks similar to a dunce cap. Once they grow larger, they begin to attack trees such as Eastern Red Cedars, Italian Cypress, Arborvitae, and more.
The bagworm’s home is an interesting and distinctive feature of the species. They construct it on top of themselves, with their feet and mouths at the opening for feeding. They then decorate their houses overtime, using pieces from their host tree. They use leaves and needles as shingles, and even an occasional berry on top! This is how they disguise themselves from predators.
By September, bagworms are done feeding, and will begin to prepare for winter. They do this by sealing their homes and entering into a month-long pupae stage. After this pupae stage, males emerge as a 1-inch long black moth with clear wings, while females transform into an egg producing grub with no wings, legs, antennae, or functional mouthparts. After males fertilize the females, the females lay up to 1000 eggs inside their sealed home, and then die. The eggs hatch in late spring, between April and May.
Treatment for Bagworm Infestations
The best treatment for a bagworm infestation is manual bag removal followed by a cycle of insecticide applications. A spray application of Bacillus thuringiensis (BT) on the foliage of the host tree is the general insecticide treatment used to control bagworm infestations. You will need to contact a local arborist for professional tree inspection, assessment, and treatment.