According to Turner (1966), the shipworm is a marine bivalve highly specialized for boring into wood. The shell is greatly reduced and the long worm-like body is protected by the wood in which it is boring; the shell is modified into a rasp for grinding the wood. Teredo can only invade new wood when they are in the larval stage during the short larval period when they are free swimming. The initial entrance hole may be so tiny it can't be seen. The first hint of problems comes after the interior is nearly destroyed and the wood disintegrates.

In the era of wooden-hulled ships, the danger of your ship literally sinking under you was very real. Quite often a ship's crew had to abandon their ship because it was "rotten" from the holes bored in its bottom by shipworms.

There are many references to the results of shipworms in the historical literature. Here are a couple of examples:

In 1502, during his 4th voyage to the Caribbean Sea, Columbus' ships survived a water spout, a hurricane, high seas, lightning and rocky reefs.