The hemlock woolly adelgid, Adelges tsugae, first appeared in the Pacific Northwest in 1924, probably from Japan. In 30 years, it was in Virginia. The primary host is hemlock, although spruce may be a secondary (alternative) host. Immature nymphs and adults, resembling tips of cotton swabs on the underside of twigs, damage trees by sucking sap from the twigs. The tree loses vigor and prematurely drops needles to the point of defoliation. If left uncontrolled, the adelgid can kill a tree in a single year. Forested areas from North Carolina to Massachusetts are experiencing significant hemlock mortality due to this pest. These small insects are brownish-red, oval, and about 0.8 mm long. Most development occurs between October and June. Crawler stage nymphs produce white cottony/waxy tufts which cover their bodies throughout their lifetime. The presence of these cottony masses on the bark, foliage, and twigs of hemlock is a sure sign of hemlock woolly adelgid.

--Sources: Entomology Publication 444-244, August 1996 S.M. Salom, Virginia Polytechnic Institute and State University, and Pennsylvania Dept. Of Conservation and Natural Resources