If you find a tiny (1/2″ long) bundle of stick-like pieces of vegetation clumped together into a “bag” that is attached to a structure, you have discovered the abandoned home of a bagworm moth larva, and the overwintering site of bagworm moth eggs. The bags consist of parts of the vegetation that the larva was eating and then bound together with silk.
In the spring, the eggs hatch and the larvae all leave and build protective cases, or bags, for themselves, inside of which they live while feeding, growing and molting throughout the summer. As the larvae increase in size, they increase the size of their bags. Eventually the larvae attach the bags to branches, trees, etc. and pupate within them. Female bagworm moths are wingless, and thus are confined to life within a bag for their entire lives. Upon emerging, adult male bagworm moths seek out the females and mate with them before perishing. After laying eggs inside their bags, females exit and die.