Bark Beetles Kills Millions of Acres from New Mexico to British Columbia

Foresters say the historic outbreak has several causes. Because fires have been suppressed for so long, all forests are roughly the same age, and the trees are big enough to be susceptible to beetles. A decade of drought has weakened the trees. And hard winters have softened, which allows the beetles to flourish and expand their range.

Hoping to keep their forests from completely dying, to earn money by selling dead and infected trees and to mitigate fire risks, landowners are scrambling to cut the pines. If enough are cut — up to 75 percent — it might leave some behind that, with less competition for water, can survive. Still, for many landowners, cutting most of the forest where they have they built their homes is painful. “I’ve literally had people in my office crying,” said Gary Ellingson, a forestry consultant for Northwest Management.

The black, hard-shelled beetle, the size of a fingertip, drills through pine bark and digs a gallery in the wood where it lays its eggs. When the larvae hatch under the bark, they eat the sweet, rich cambium layer that provides nutrients to the tree. They also inject a fungus to stop the tree from moving sap, which could drown the larvae. That fungus stains the wood blue.

“The Latin name is Dendroctunus, which means tree killer,” said Gregg DeNitto, a Forest Service entomologist in Missoula, Mont. “They are very effective.”