Because a single piling may contain several thousand ship- 
worms, it may be literally honeycombed (fig. 2). In such situa- 
tions, tunnels may be no more than 14, of an inch in diameter and 
only a few inches long. Under the most favorable conditions, how- 
ever, the tunnels may reach a diameter of 1 inch and a length of 
4 feet. 
The genus Martesia also contains a number of destructive 
species. They differ from the shipworms in being clam-like. The 
young are also free-swimmers and seek out and attack submerged 
wood, making small, inconspicuous entrance holes. Once inside the 
wood, they grow until they are about 25 mm. in diameter and 
60 mm. long. As they grow, they enlarge their cavities to accomo- 
date their bodies. Members of this genus are found along the 
shores of the Gulf of Mexico. 
Damage to pilings by shipworms can be prevented by impreg- 
nation of the wood with a suitable preservative. Coal tar 1 
creosote is recommended for treating waterfront timbers of 
Douglas-fir and southern pine. Copper naphthenate is usually 
used for the protection of wood in boats. Coatings of paint and 
metal are also effective as long as they remain intact. 
F-519930 
FIGURE 2.—Cross-section of a piece of timber riddled with tunnels made 
by a molluscan shipworm of the genus Bankza. 
11 
