56 Dwellers of the Sea and Shore 



grow to the size of a pinhead they seek lodgment on 

 pilings and other submerged timber, and there start 

 their burrows. For a short distance from the entrance, 

 each burrow is perpendicular to the surface; it soon 

 turns, however, and aligns itself with the grain of the 

 wood, although with more or less of a twist. Regard- 

 less of how numerous these burrows may be, the occu- 

 pants never touch each other. Always there remains 

 a thin partition between the individuals infesting the 

 wood. The shipworm mines its tunnel to accom- 

 modate its growth. As the burrow increases in length 

 it increases somewhat in diameter, but the original 

 point of entrance always remains the same. This open- 

 ing is so minute that it easily escapes notice and the in- 

 festation is generally not detected until the destructive 

 work of the animal is well advanced. It is through this 

 orifice that the shipworm thrusts out its paired, siphon- 

 like tubes to strain the water for food. 



Ever since man began to build ships and wharves 

 he has had to contend with this diminutive monster. 

 So effective are its ravages that it can ruin utterly 

 within the space of a few months that which takes 

 years of labor and millions in money to construct. In 

 the upper part of San Francisco Bay the damage dur- 

 ing the years 19 19 and 1920 resulting from the activi- 

 ties of the shipworm has been estimated to exceed 

 $15,000,000. This estimate was placed solely on the 

 damage to docks and piers; what the total losses to 

 shipping and harbor construction of all our ports dur- 

 ing every year may be Is not determined; it is agreed, 

 however, that the amount is so stupendous that Its 

 significance would be lost on the average mind. Here- 



