The hemlock woolly adelgid (HWA), a tiny, aphid-like insect, is a major threat to hemlock trees in West Virginia. The HWA is native to Asia but was accidentally introduced into the eastern United States in the 1950s. Because it has no natural enemies here, it has spread quickly along the East Coast.

This insect feeds on the tree's sap. Infestation is usually fatal, often killing the hemlock tree in just four to six years. The HWA was first found in West Virginia in 1992 in four eastern counties. By the 2020s, it had spread to almost every county.

Hemlocks are important for their beauty, especially in places like Cathedral State Park and Blackwater Falls State Park.

Scientists are trying to fight the HWA by introducing predatory beetles from Asia (biological control) and treating important trees with pesticides injected into the wood. The West Virginia Department of Agriculture (WVDA) has a program to treat "high-value" infested trees.