... the bagworm larvae of many species create these cases as they grow. In July I watched many of them outside a hospital in Annapolis as they moved through evergreen and cedar trees, grazing the needles. When ready to enter the pupa stage they attach the case firmly to a twig or otherwise glue it to an object (fence, building). This one belonged to a male who emerged at the bottom, leaving a telltale bit of effluvium or pupal covering projecting from the escape hole. In many or most species of bagworms the female remains in the case, attracting a male by emitting a pheromone lure. They mate without the male ever seeing the female. She lays her eggs in the case and dies. Upon hatching the first instar caterpillars leave the case, disperse, and begin fashioning their own cases as they feed. In colder areas the last generation of the season (when there is more than one per year) overwinters in the case.