You may see some dangling, brown, bag-like icicle shaped objects hanging from your Leyland cypress or other conifer, but don’t be fooled. They are not pretty decorations for the season, they may be the cocoons of Bagworms.
Bagworms, Thyridopteryx ephemeraeformis, are common landscape pests because they feed on many of the most common ornamental plant species. They can be readily identified by the cone-shaped bag they spin from silk and embed with bits of host plant and other debris. The bags range in size from 1⁄4 inch to over 2 inches to accommodate the growing caterpillar inside (hence the name).
Momma bagworm never leaves her house. She stays wingless, legless, and grub-like. Poppa bagworm gets around a bit more as a small, brown hairy moth with dark wings that clear with age. In fall the female lays hundreds of spherical or oblong eggs within her pupal cast skin that overwinter and hatch in spring. Precisely why you want to scout for them this winter, cut them off when you find them and dispose of them (not in the compost pile), so they don’t hatch out and grow the population in spring.
Bagworms can feed on many plant species but are most common on conifers such as leyland cypress, arborvitae, cedar, juniper, and pine. Defoliation for multiple years can reduce tree growth or cause sparse foliage and poor appearance by defoliating branches that alter plant shape and foliage density. Large sections of evergreens may be killed outright. In addition, the brown bags can become very noticeable and unsightly in large numbers. I’ve seen them develop bags in rose bushes, so do some reconnaissance while you are getting a breath of fresh air out in the garden. It’s also a great mission to give visiting children over the holidays, plus it gets them outside.
Silk is strong and this insect spins silk into anchoring and building their bag of protection. Bags can be mechanically removed by pruning infested branches or hand picking bags. 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. Just pulling the bag to remove it not only is tough to do, the silk band may slide along the twig and shear off the needles. However, If not removed, the silk bands sometimes girdle the twig, which causes it to eventually die and break off at that point. Each bag could contain 1,000 eggs so picking them off in fall and winter could make a big difference in spring.
Other garden helpers are available to help, and they work for food, as in consuming the bagworm for lunch. It’s Ecological Pest Management in action. Bagworms are parasitized by several kinds of parasitoids, including parasitic wasps (they are really tiny wasps, not the larger wasps that we’re familiar with). Even European sparrows get in on the lunch line. In many cases natural parasitism and predation may keep populations below noticeable damage levels. In fact, studies have shown that parasitism rates of bagworm were 71% higher in shrubs that were surrounded by flowering non-grass plants than in shrubs that lacked flowers.
It’s a jungle out there for sure, but a pretty one so get out into it so you don’t miss anything interesting! Contact me at minda_daughtry@ncsu.edu with any questions.
