borer, name applied to various animals that are injurious because of their ability to penetrate plant or animal tissues. Among insects, some borers are beetles, e.g., the flatheaded apple-tree borer, a serious pest of many shade and fruit trees; the roundheaded apple-tree borer; and the bronze birch, locust, elm, shot-hole, and poplar borers. Other boring insects are moths that are harmful in the larval stage, e.g., the peach, currant, squash, lilac, and southern cornstalk borers and the European corn borer. Marine borers include the boring sponges, certain marine worms, and some bivalve mollusks, e.g., the rock borer, the shipworm, and the piddock, which are thought to secrete acids that dissolve rock and other substances. The hagfish, or borer, is a marine pest that burrows into the bodies of other fish.