Late spring and early summer are when we start seeing our first samples of bagworm infestations.  Severe infestations can seriously damage the beauty and health of host plants, especially juniper, arborvitae, hemlock, fir, pine, and spruce species. Bagworms can also attack cypress, black locust, willow, sycamore, apple, maple, elm, poplar, oak, and birch. Severe defoliation may occur followed by the death of the plant when large numbers of bagworms are present. They feed on buds and foliage, sometimes chewing needles almost in two. They have one generation a year and over-winter as eggs in the female bag. There can be as many as 300-1000 eggs in a single bag. Hatching occurs in May-June depending on the weather. When the larvae hatch they leave the bag, spinning down from it by a strand of silk that often acts like a parachute to carry them to new hosts. There they immediately spin themselves a bag, which becomes covered with plant debris from the host as they crawl around feeding. This camouflages them so well that they often go unnoticed until considerable damage has been done. In fact, many homeowners fail to notice them until they have matured and permanently glued themselves to a stem. At that point, they have quit feeding and the damage has been done for the year. Chemical control is best achieved when affected plants are sprayed twice a year, once in May and once in June.