Bagworms are voracious feeders once they reach a critical size. Evidently we are at that critical size now which is about a month and a half behind when they usually become a problem. Bagworms are the tree ornaments of nature. The caterpillar forms and lives in its own pouch domicile. The bag is spun to create an extremely tough structure and they continue to add to the size as they increase their size. They live in, mate in and feed from the comfort of their living room. When they attach to a branch they resemble a little ornament hanging from the tree. However, gain no satisfaction from their decoration because these buggers can defoliate a spruce, arborvitae, pine, cedar, etc. short order.
Observing your plants will be the best defense to thwart off an invasion. Stay diligent beginning in May and check periodically. They begin as a hatchling from the overwintered bag (with as many as 300 siblings) and are very small. Their small size and an incomplete bag make them susceptible to what ever you decide to use as your offense. For more detailed information and control measures see the University of Kentucky publication: Bagworms on Landscape Plants
