264 TIMBER 



the grain, but it will sometimes work right across the 

 grain ; the tunnels are distinct from each other. 



The teredo gradually increases in length and thickness, 

 and although on the outside of the timber, if closely 

 examined, only small holes about the size of a pin head 

 are to be seen, yet it may be completely riddled (see 

 Fig. 36). An average-sized teredo is to | inch diameter 

 and 15 inches long, but specimens up to 4 ft. in length 

 and upwards have been obtained with a diameter of over 

 half an inch, and quite recently, in the Transactions of the 

 Eoyal Society of New South Wales, Mr. H. D. Walsh, 

 M.I.C.E., stated that he had taken a teredo from timber in 

 one of the northern ports of New South Wales 6 ft. long 

 and nearly f inch in diameter. 1 The teredo usually passes 

 round knots and rarely crosses a seam or joint in the wood, 

 and must always command the entrance to its tunnel and 

 have free and permanent access to pure sea water, other- 

 wise it can only exist for a short time, although Mr. 

 J. W. James, M.I.C.E., mentions that he found several still 

 living, but very weak, in timber which, after being taken 

 out of the water, had lain exposed to the tropical sun for 

 two months. The teredo works from a little above low 

 water, or say half-tide level, down to the ground, and 

 timber 25 ft. below lowest water level has been found 

 attacked. It does not devour the wood, but passes it 

 through its body and is very rapid in its work. A young 

 teredo has been found in wood submerged eight days. It 

 thrives best under the influence of heat, and in a tropical 

 climate is most destructive ; 6-inch timber has been 

 destroyed in six weeks in the Gulf of Mexico, and piles 

 12 inches by 15 inches have had to be replaced after six 

 months' service in the same district. 



1 The Engineer, llth October, 1907. 



