Bagworms

(click on image to enlarge)

Bagworms are insects that form bags of silk, twigs, and leaves.  They feed on over a hundred different species of trees and shrubs, including arborvitae, Juniper, and Cedar.  Bagworms are actually moths - it's the larvae of the moth that forms these bags.

Bagworms have just one generation per year.  In June, the eggs that have over wintered hatch.  The larvae emerge and form new bags, feeding on the foliage of the host plant.  When they mature, the pupate and the adult male leaves the bag to find the female.  After mating, the female lays eggs in her bag and dies.  The eggs over winter in the bag until the next spring.

If there are only a few plants infested, the bags can be physically removed and destroyed.  The larvae can, however, severely damage the plants if infestation is high.  In this case, insecticides should be used.

photo provided by: www.ppdl.purdue.edu