Bagworms are the larval stage of a moth. These caterpillars, which are dark brown with a yellow head and yellow and black spots on the body, build and remain inside spindle-shaped bags. The bags are generally around two inches long and are made of silk from the caterpillar and bits of leaves or twigs from the tree it has eaten.

Bagworms attack trees, both deciduous and evergreen, but are most often found on juniper, cedar, arborvitae, pine and spruce. The larvae begin feeding and constructing their bags in early summer, growing in size until they become adults in fall.

Bagworms damage trees by stripping the foliage. If an infestation is large enough, the tree may eventually die. When the larvae are young, the bag is upright on the tree branch and looks like a cone. As the larva grows it moves about feeding and carrying its bag with it. It adds bits of material from the host plant to its bag. The bag on a juniper or other evergreen may even be mistaken for part of the tree itself.

A satisfactory control for a small infestation of bagworms is to pick the bags off trees by hand in fall, winter or early spring. For larger infestations it may be necessary to use an insecticide labeled for controlling bagworms.