A bark beetle.
bark beetle definition by Webster's New World
Webster's New World College Dictionary Copyright © 2010 by Wiley Publishing, Inc., Cleveland, Ohio. Used by arrangement with John Wiley & Sons, Inc.
any of a number of small weevils (family Curculionidae), the larvae and adults of which burrow under the bark of trees, esp. conifers, and feed on the inner bark, sometimes causing extensive damage
bark beetle definition by American Heritage Dictionary
Any of various small cylindrical beetles of the family Scolytidae that burrrow along the surface wood directly beneath the bark of trees, causing extensive damage.