Often several boards are damaged by a single pocket.

In grading lumber, pitch pockets are classified as small, standard, and large, depending upon their width and length.
INSECT INJURIES[37] [Footnote 37: For detailed information regarding insect injuries, the reader is referred to the various publications of the U.S.Bureau of Entomology, Washington, D.C.] The larvae of many insects are destructive to wood.

Some attack the wood of living trees, others only that of felled or converted material.

Every hole breaks the continuity of the fibres and impairs the strength, and if there are very many of them the material may be ruined for all purposes where strength is required.
Some of the most common insects attacking the wood of living trees are the oak timber worm, the chestnut timber worm, carpenter worms, ambrosia beetles, the locust borer, turpentine beetles and turpentine borers, and the white pine weevil.
The insect injuries to forest products may be classed according to the stage of manufacture of the material.

Thus round timber with the bark on, such as poles, posts, mine props, and sawlogs, is subject to serious damage by the same class of insects as those mentioned above, particularly by the round-headed borers, timber worms, and ambrosia beetles.