A bagworm suspended from a branch. Image: Eric R. Day, Virginia Tech, Bugwood.org
Bagworm infestations can be severe and unsightly. Image: Pennsylvania Department of Conservation & Natural Resources, Bugwood.org
It’s a pinecone! It’s a dying branch! It’s an … insect? Bagworms are masters of disguise and can easily confuse those who are unfamiliar with its cryptic appearance.
Not really worms, bagworms are actually moth larvae that feed on conifers and occasionally some hardwoods. They cover themselves in a silken bag composed of needles or leaves from the tree on which they’re feeding. They are fairly common, and although they seem harmless, they can cause substantial damage to ornamental conifers such as junipers, Leyland cypress, baldcypress and arborvitae.
As they feed, the larvae and the bag providing their cover get larger and larger. They pupate inside the bag suspended from a branch. After development, adult males emerge and fly away. Females, however, are wingless and doomed to stay in their bag, producing a pheromone to attract their winged counterparts.
Bagworm infestations can be severe and may cause branches, and sometimes the entire tree, to die. Luckily, you can combat infestations by hand-removing and destroying the bags of growing larvae or adult females (in the growing season and winter, respectively) or by applying an insecticide in the early summer when larvae are feeding.
So, pack your bags, bagworms. You won’t be moving on to greener pastures.