A bark beetle is one of approximately 600 species of beetle in the family Scolytidae that are known for their ability to bore into the cambium layer of trees to lay eggs and reproduce. Bark beetles attack only living trees, not dead trees or cut lumber.

Bark beetles are prone to attack trees that are already weakened by disease, drought, smog, and physical damage. Healthy trees put up defenses by producing sap, which may not be sufficient to stave off infestation under some conditions, particularly drought. Pulling the bark from old and dead tree trunks, especially elm, you are fairly certain to find the home of the bark beetle. Beetles will emit pheromones to attract other beetles, which are drawn to target trees and may result in heavy infestation and eventually death of the tree.