Eggs hatch inside the bag in the spring and the young larvae begin feeding and constructing new bags with the foliage of the host plant. Typically, they feed on the needles of arborvitae, juniper, and hemlock. The larva enlarges the bag as it grows. When it becomes full-grown, it stops feeding and firmly attaches the bag to a twig. Pupation takes place inside the bag in late summer.
Winged males emerge several days later and mate with the wingless females in the bags.
The female moths lay eggs and die. The eggs overwinter inside the bag during the winter and hatch out the following spring. Handpick and dispose of the bags by dropping them in a container of soapy water. Other insecticides are available.