Here we have the inspiration for the movie tremors. Teredo clams are worm-shaped clams that use shell-shaped jaws to chew through wood. Because these clams do look an awful lot like worms, and perhaps because the idea of a wood eating clam is too strange to believe, people refer to these animals as shipworms or termites of the sea. But no. These are marine clams that eat wood, creating something called wormwood. Here's a teredo clam, with its worm-like body and head of shells: 
A special enzyme allows the clams to digest cellulose, but most species supplement this wooden diet with planktonic protein. The clams line their tunnels (which can be up to 6 feet long in some species) with a white calcareous substance. The most common species of teredo in Puget Sound is Bankia setacea, which can grow to be 1/2 inch thick and 3 feet long and eat up to 3/4" of wood a day. Shipworms have wreaked havok on ships and pilings for as long as mankind has been putting wood into the water. 18th century shipwrights used copper sheathing to protect their hulls from teredo clams; nowadays people paint submerged parts of their boats with a copper paint to prevent the clams from establishing. Last year we got some teredo wood tables made by the folks at Trinity River Marine from old boomsticks at the Port Gamble mill. (Boomsticks are the logs used to hold log booms together). A wormwood piling: 
Our table:
The white calcareous substance that the clams use to line their burrows: 
Let us know if you want to buy a teredo table for yourself and we'll put you in touch with the fabricators!