A. First, I need to make sure we are talking about the same critter. Bagworms are caterpillars that make cocoons shaped like a diamond. They are not the critters that create webs that resemble large spider webs. The confusion might arise because the common name "bagworm" is sometimes used to refer to any number of caterpillars. Extension agents refer to this creature by its proper Latin name, Thyridopteryx ephemeraeformis.

Bagworm eggs hatch toward the end of May or first week in June. The baby worms are about 1/8 of an inch long. Instinctively, they begin to test the strength of their silk by spinning a silk thread and hanging around. Spring breezes catch the wee worms and blow them to greener pastures. (For a baby bagworm, greener pastures are a long line of Leyland cypress trees.)

If a bagworm is lucky enough to land on a suitable host plant, then it spins a silk cocoon. The cocoon serves as protection from predators, sunlight, pesticides and such. Foliage from the host is cleverly incorporated into the silk cocoon.

As the bagworms feed on the foliage of the plant (usually a juniper or arborvitae), they grow and enlarge their silk protection. Homeowners finally spot these pests in August or September. By then, the damage is also very obvious.

Young caterpillars are easy to kill. Mature caterpillars with a protective silk shell are difficult to kill. Therefore, launch the pesticide assault in late May or early June. Products containing Bt (Bacillus thuringiensis), such as DiPel or Worm Whipper, can kill the youngest of the pests, but do not work very well on mature ones. The products are not contact insecticides, so have to be eaten by the caterpillar. Simply spray the Bt on the foliage and let the bagworms nibble. After a couple of bites, they develop a stomachache that won't go away. This target specific, noncontact type of pesticide bypasses the protective cocoon and is very safe to the applicator and surrounding environment.

Contact insecticides such as Sevin, Malathion or Orthene are also more effective when the caterpillars are young. By the end of August or September, bagworms are nearly invincible.

Worth noting: Bagworms were the original inventors of the ghillie suit, the camouflage get-up hunters and snipers wear that makes them look like Swamp Thing. Another name for the ghillie is yowie. Fittingly, this is also what homeowners might say in September when they realize how many bagworms are eating on their Leyland cypress tree.

For more about bagworms, go to www.ces.ncsu.edu/depts/ent/notes/O&T/trees/ort081e/ort081e.htm or call your local Cooperative Extension agent.