Bark beetles are always living in forests. They kill clusters of trees, providing dead snags for wildlife habitat, and helping to recycle nutrients from dying trees. They are also food for other insects and woodpeckers. Periodically, bark beetle populations boom when environmental conditions favor the beetles.References
Jeff DeLong: Pair of bugs threatens Nevada forests. Reno Gazette-Journal, August 10, 2009
USDA Forest Service: Sustaining Alpine and Forest Ecosystems. Forest Insects.