Bagworms are pests on many kinds

Bagworms are pests on many kinds of conifers and deciduous trees, though they’re most frequently found on arborvitae and junipers. The dark brown bagworm caterpillars are 1/8 to 1/4 inch long when they first hatch, eventually reaching one inch long. As the insect feeds, it creates a silken case covered with the leaves made from the host plant, binding the bag together and attaching it to the plant with a silken thread. The bag will look different depending on the host plant. For example, the bag on a maple will look different from a bag on an arborvitae. Since bagworms add plant materials to the top of the bag, the freshest and greenest material is on the top of the bag. When you see a bag that is entirely brown, the insect inside has stopped feeding or is dead. The bags are ultimately 1 ½ to 2 ½ inches long. Once a plant is infested, populations can grow quickly.