The sole object of boring into the wood is to obtain shelter.
Although shipworms can live in cold water they thrive best and are most destructive in warm water.

The length of time required to destroy an average barked, unprotected pine pile on the Atlantic coast south from Chesapeake Bay and along the entire Pacific coast varies from but one to three years.
Of the crustacean borers, _Limnoria_, or the "wood louse," is the only one of great importance, although _Sphoeroma_ is reported destructive in places.

_Limnoria_ is about the size of a grain of rice and tunnels into the wood for both food and shelter.

The galleries extend inward radially, side by side, in countless numbers, to the depth of about one-half inch.

The thin wood partitions remaining are destroyed by wave action, so that a fresh surface is exposed to attack.