At one of our recent library programs, a homeowner asked me to identify an unusual creature found in his home. His specimen bag contained several flattened, gray, watermelon seed-shaped cases about one half inch long, that were collected from the walls of an outdoor shed. A few years back, my family had moved into an old house that had hundreds of these critters stuck to the inside walls, and I become familiar with this Florida Critter - the plaster bagworm. It is a curious insect that causes occasional damage to certain clothes and fabrics. Information for today's column comes from a new "Featured Creature" entry recently added to this popular University of Florida Entomology Internet website.
The plaster bagworm (Phereoeca dubitatrix) is frequently misidentified. While the first record of this species came from the Virgin Islands, its feeding habits in Florida helped to distinguish it from other species of flat case-bearing moths. The "homes" these creatures construct often attract attention when found hanging on walls of houses in south and central Florida. However, usually this larval or pupal cases are empty. Adult plaster bagworms are moths similar in appearance and closely related to clothes moths.
The plaster bagworm requires high humidity to survive. Because of this, they are not commonly found inside air conditioned buildings. The need for high humidity limits its range to many parts of Florida and Louisiana, as well as in Mississippi and North Carolina. Other related species of case-bearing moths are found in Florida, and are present in the coastal areas of Alabama, Georgia, South Carolina, Texas and Virginia and many other parts of the world. Due to international movements of commercial products, new species of these case-bearing moths could enter Florida in the future.
Plaster bagworms are easily seen on light-colored walls. Close examination inside the house may reveal bagworms attached to the underside of chairs, bookcases, and other furniture. They are often found along the edge of rugs, near baseboards, or on the lower edges of walls. Bagworms are quite common in garages and underneath buildings. The larvae mainly feed on spider webs; however, they will also feed on fabrics made of certain natural fibers.
There is incomplete information about the life cycle of this insect in Florida. A related species in Panama that lives in non-air-conditioned room temperature may closely approximate the habits of our Florida plaster bagworm. The adult moth lays eggs that take more than 10 days to hatch. Larval bagworms will mature in 50 days and molt seven times before they pupate. They remain in the pupal stage for 11 to 23 days. So, the entire cycle from egg to adult averages 62-86 days.
After mating, females lay their eggs on crevices and the junction of walls and floors. They are cemented on debris that is found in areas with suitable food. Two hundred eggs may be laid by a single female over a period of a week, after which she dies. Eggs are soft, pale blue, and almost microscopic ( 0.4 mm) in size.
The larvae of bagworms live in the characteristic gray, seed-shaped case, which measures about one-half inch long. The case is constructed of silken fiber and sand particles, lint, paint fragments, and other debris that is found. This protective home has a slit-like opening at each end, and the tiny caterpillar is able to move around and feed from either end.
The larva is not usually seen by most people. The case that it carries around wherever it feeds is what is immediately recognized. It can be found under spiderwebs, in bathrooms, bedrooms and garages. Cases can be found on wool rugs and wool carpets, hanging on curtains, or underneath under buildings, hanging from subflooring, joists, sills and foundations; on the exterior of buildings in shaded places, under farm sheds, under lawn furniture, on stored farm machinery and on tree trunks.
The case is constructed by the first stage larva. In making the case, the plaster bagworm builds a silken an arch. Very small particles of sand, soil, iron rust, insect droppings, arthropod remains, hairs and other fibers are added on the outside. The inside of the arch is lined exclusively by silk, and is gradually extended to form a tunnel. The larva stays inside this tube which can be opened at either end. After the case is constructed, the larva starts moving around, pulling its case behind.
With each molt, the larva enlarges its case. Later cases are flattened and widest in the middle, allowing the larva to turn around inside. A fully developed larva has a case 1/4 to 1/ 2 inch long and 1/16 to 3/8 inches wide. Both ends of the case are identical, and are used by the larva as a place to hide. When disturbed, bagworm larva move inside the case, and pull the lower side up to enclose the whole worm. It is very difficult to open this case from outside.
A fully developed bagworm caterpillar is about 1/4 inch long. It has a dark brown head, while the rest of the body is white, except for some darkened plates above and below the head. It is thought that these hardened plates protect the developing insect larva from natural enemies when it reaches out of its case to feed or move. The larva has three pair of well developed, brown legs. It also has several "false legs" with hooks on their ends. These hooks help it to walk inside its case, and to hold on to its protective home when the larva moves its head and thorax outside. The bagworm uses its true legs to walk on the floor or walls.
The larva will mature into an adult moth after it goes through a pupal resting stage that occurs inside the case. The larva walks up an upright surface and attaches the case at both ends with silk. The new adult moth emerges at mid-day, leaving the pupal shell outside the larval case. Adult female moths have a wing span 1/ 2 inch long. They are gray with four spots on the front wings, and a brush of long, lighter gray hairs along the back edge of the back wings. Males are smaller in size (wing span: 3/8 inch) and thinner than the female, with a less obvious markings on the wings. Adult moths do not feed. Adults at rest hold their wings over the body. They fly fairly well, but usually rest on walls, floor edges, or on webs of house spiders.
The most common food of the plaster bagworm in Florida is old spider webs, which are consumed in large quantities. Webs of insects such as booklice and webspinners from tree trunks are also suitable food. Old larval cases of its own species are sometimes chewed as well. Even though small portions of dried insects are found attached to its case, this insect has not been observed to feed on dried insects. Plaster bagworm larvae do not eat cotton fiber products, but woolen threads are eagerly consumed by the larvae. Another researcher fed the larva with dead mosquitoes and hair.
Due to its food habits, the plaster bagworm has potential as a household pest. However, regular cleaning practices, increased use of air conditioning in houses, and fewer wool clothes in this part of the country. have decreased the incidence of the plaster bagworm. The use of routine pesticide applications in cracks and crevices for household pest control have also reduced the chances of finding this critter in our Florida homes. Manual picking or vacuuming of cases and spider web removal should be enough to keep this species under control. If needed, specific pesticide recommendations can be obtained from our office. Outside, there is no need for control measures, as these insects perform as valuable scavengers. A braconid wasp [Apanteles carpatus ] has been found to parasitize the larvae of case-bearing moths, killing the larva before pupation.
If you need additional information on plaster bagworms or other household pests, visit our Master Gardeners, or call or stop by our office. For those with other questions about Florida Yards, our office holds Master Gardener Clinic hours at the Extension office (1028 20th Place, Suite D, Vero Beach) every weekday morning and most afternoons, Wednesday morning at the Sebastian Library, and the second and fourth Saturday of the month at the ELC. Our phone number is 770-5030, and you can leave a message after hours. Happy Valentine's Day!
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