4 N. J. Agricultural Experiment Stations, Circular 139 



widespread over a large part of San Francisco Bay. Before owners 

 were aware that anything was wrong, the borers had completely cut 

 off at the mudline the piling of many piers, terminals, and other 

 marine structures (fig. 1). Based upon the costs of repairs and re- 

 placements made necessary through these attacks, a careful estimate 

 of the damage done during 1920 and 1921 in San Francisco waters 

 alone gives a figure in excess of $15,000,000. 



Fig. 1. Municipal Wharf and House, Benicia, California 



Collapsed October 7, 1920. (Reproduced by courtesy of San Francisco Marine 



Piling Committee from their report, 1921, pi. 1, fig. 3.) 



The two most important reasons why the European pileworm is so 

 much more dangerous than the native species are : first, that it in- 

 vades the brackish water area and comes much closer to fresh water 

 than do other borers ; and second, that it requires but a very short time 

 to reach sexual maturity, and in a single season produces enormous 

 numbers of young. 



What it is and How it Lives 



Before describing the outbreak of Teredo navalis in Barnegat Bay 

 last summer, let us consider briefly some of the most important points 

 in the make-up and the life history of the animals. The figure on the 

 title page shows a number of young specimens of Teredo navalis, sexu- 

 ally mature, as removed from their burrows. Three specimens of the 

 native shipworm, Bankia fimbriata, are shown above for comparison. 

 Note the two delicate shells which partly cover the front or anterior 

 end, and between which lies the foot (fig. 5). By far the greatest 



