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 f 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.^ 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. 
^ Tlie Engineer, lltli October, 1907. 
