The insects have killed millions of trees in the eastern U.S. and threaten 80 million eastern hemlock trees in Wisconsin. A single egg sac may contain as many as 300 eggs. Hundreds of thousands of the insects can feed on the trees with their needle-like mouth parts, said PJ Liesch, an entomologist with the University of Wisconsin-Madison Division of Extension.
“It’s a whole bunch of them ganging up on the trees,” Liesch said. “Together, that combined feeding damage over time causes those hemlock trees to decline and ultimately die.”