The bags are often mistaken for cones
bagworms
Thyridopteryx ephemeraeformis
The bags are often mistaken for cones
DESCRIPTION Bagworms are actually the caterpillars of short-lived moths. They leave a very noticable sign of their presence, creating a tough bag out of bits of twigs and leaves and their silk. The adult female doesn't lay eggs, the larvae offspring emerge from the parent's body in midspring. They form new bags as they feed, then attach the bag to a branch in late summer to pupate.
HOST PLANTS Bagworms can attack most trees and shrubs, most commonly arborvitae, juniper, elm, boxelder, birch, and willow.
CONTROL Handpick bags and destroy them in late winter. The silk that tied the bag to the branch should be removed as it will girdle that spot. Insecticidal soaps, Bt or other labeled insecticides can be used in the spring to kill the larvae.