Gribble    Limnoria lignorum                            Teredo     Bankia setacea

This chunk of damaged wood at the Boston Harbor Marina hasn't been attacked by pollution or a mad carpenter.  Rather two inconspicuous animals have used the wood for both a home that protects them from predators and as a source of food.

The small burrows at the top of the piece of wood have been made by a very small relative of crabs, shrimp and pill bugs called a Gribble. It burrows near the surface of submerged wood such as piling, floats or boats. Unlike termites that use special gut bacteria and other microorganisms to digest wood, the Gribble uses the enzyme cellulase. Since the larvae don't swim very well, dispersal occurs from adults inside of drifting wood.  Gribbles can be found throughout the cold waters of Puget Sound and other waters of North America.

The second animal is the Teredo or Shipworm.  Housed in white calcareous tunnels up to 3/4 of an inch in diameter and three feet long, this clam burrows into the heart of a piece of wood. Like other clams, the Teredo uses its muscular foot for digging.  It anchors the foot at the bottom of the tunnel and twists its small raspy shell against the wood, drilling ever deeper.  While it uses some of the wood for food, digesting it with cellulase, it gets most of its nutrients from straining plankton from the water.  Drifting larvae seek out new sources of wood helping spread the clam throughout the colder waters of the Northern Hemisphere.