Evergreen Bagworm

Bagworm on Red Cedar after a snow fall.

     The Evergreen Bagworm (Thyridopteryx ephemeraeformis) is not usually noticed in natural areas, but may cause aesthetic concerns in landscape settings, especially among non-native plantings and where there are few predators of them. Even then, most people never even notice the cleverly concealed caterpillar in its bag. Although they prefer evergreens such as cedars and arbor vitae, they have been found on over a hundred different tree species, including many deciduous trees, always using parts of the tree to cover their silken bags. If causing a concern in the home landscape where there are few natural controls, the bags can be snipped from branches before June and dropped into soapy water to control their numbers. 
     The life cycle is most unusual, with the caterpillars feeding from their hidden homes through the summer, pupating for a couple of weeks, before then changing into adult moths. This usually happens during September or very early October, and only the charcoal-colored males with transparent wings ever leave the bags. The males seek out their mates for about 2 weeks before they die. The female sacrifices everything in order to be an egg production machine. She has no wings, non-functional legs, almost no eyes, and lacks even antennae and mouth parts. Her sole duty is to send out pheromones to attract a male and then lay eggs (200-1000 of them) inside her bag before dying.
     The eggs remain hidden in the bags, hanging throughout the winter. By the beginning of June, the newly born caterpillars will emerge from the bag, drop down on silken threads, and then either "balloon" with the wind to another plant, or drop down and climb up a plant to build their own bags and start the cycle all over again, often passing the mummified remains of their mother on their way out.

On small isolated, mostly nonnative plantings, bagworm numbers can buildup and cause defoliation.