Any one of a number of species of mainly wood-boring beetles. Bark beetles are cylindrical, brown or black, and 1–9 mm/0.04–0.4 in long. Some live just under the bark and others bore deeper into the hardwood. The detailed tunnelling pattern that they make within the trunk varies with the species concerned, and is used for identification.

Most bark beetles live in forest trees; some, however, attack fruit trees. Generally, but not always, dead or dying timber is attacked. Some species transmit pathogens, for example, the fungus that causes Dutch elm disease.

Examples include the birch bark beetle Scolytus ratzeburgi and the greater fruit-tree bark beetle S. meli.

Classification
Bark beetles are in the families Curculionidae or Scolytidae, order Coleoptera, class Insecta, phylum Arthropoda.

The social habits of members of this family are diverse. Various degrees of polygamy and monogamy are practised; simple unorganized and intensive polygamy; organized polygamy, and a gradual reduction in the number of adult females per male. For example in the genus Xyleborus a single male may be associated with 60 or more females; in Ips one male is associated with two females. The genus Scolytus is monogamous.