236 



July 1. All were found to he heavily infected and several broke under their own weiyht 

 at or near the level of the mud line when lifted up on the wharf (fig. 87). 



Sections of a timber planted July 1 (fig. 88) show that the 6 by 8 inch timber 

 had been completeh- riddled at the mud line by Teredo. This timber had been ex- 

 amined on August 4 and showed no infection at that time. Thus in 4 months, or 

 at the most 126 da\s, this timber was utterly destroyed at the nuul line. A similar 





Fig. 87. Breaking point of a 6 x 8 Douglas fir timber planted at Southern Pacific wharf, Port Costa, 

 California, July 1, 1920. First larvae detected at this locality on August 4. Timber removed December 

 8, 1920. Destroyed by Teredo navalis. 



attack on a 1 2-inch pile would penetrate three-fourths of its cross section and reduce 

 its efficiency below the danger line. 



The rate of destruction of timber b\- Bankia setacea is generally slower than in 

 the case of Teredo navalis. Its larger, more rapidly driven burrows occur typically 

 more sparsely than the burrows of Teredo, and the substance of the wood is not so 

 thoroughly destroyed. Piling in dolphins of the Alameda Mole, driven in February, 



