The hemlock woolly adelgid is a very small, aphid-like insect that threatens to decimate eastern and Carolina hemlock trees over most of their natural range, including West Virginia. A native of Asia, the hemlock adelgid was first reported in the western United States in 1924 and in the east in the mid-1950s. Lacking natural enemies in North America, this exotic pest now infests the East Coast hemlock forest from Maine to Georgia and has been found as far west as Tennessee. In 1992, the West Virginia Department of Agriculture detected the insects in four counties: Grant, Pendleton, Hardy, and Hampshire. By the 2020s, the hemlock adelgid had spread to all but two West Virginia counties: Brooke and Hancock.

Hemlocks comprise about one percent of the forested land statewide and up to nine percent in individual counties. Recreation areas where hemlocks are in abundance have been of special concern. Those include Cathedral State Park, where the ancient hemlocks are the main attraction, and Blackwater Falls State Park.

Infestations of eastern and Carolina hemlock are generally fatal, with tree death occurring from the sapfeeding adelgids within four to six years. Concerns for ecologically important hemlock habitat have prompted experimentation with the introduction of a biological control agent (a predatory beetle from Asia) and treatment of individual trees with injected and implanted pesticides.

In 2011, the Department of Agriculture (WVDA) launched a project to treat hemlock trees on private property. The WVDA addresses the problem by treating "high-value and high-visibility infested hemlocks with Imidicloprid."