Editor's note: Today's feature is the second spotlighting the eastern hemlock, which is threatened by an invasive insect. Hemlock trees in Pennsylvania were used by Native Americans for medicinal purposes and later, loggers relied on the massive trees for lumber. The trees' unique bark hue was also used for tanning of leather. Given that, it's no wonder the hemlock is Pennsylvania's state tree. Today, the hemlock is threatened by an invasive species â the woolly adelgid â which has decimated populations of eastern hemlocks in more southern states, and is threatening to do the sa...