94 DEPARTMENT OF THE NAVAL SERVICE 



8 GEORGE V, A. 1918 



destruction than has been ascribed to its ally Limnoria lignorum, which Murphy^ 

 states can, when abundant, destroy soft timber at the rate of half an inch or more 

 every year. Stearns^ has recorded two interesting examples of the work of Teredo. 

 He states that "upon the seafront of San Francisco I have known piles of Oregon 

 pine and fir over a foot in diameter rendered worthless in eighteen months." Dt. Dall 

 is quoted by Stearns as having noted a case of the destruction of the supports of a 

 .«raall pier made of piles 6 to 8 inches in diameter near the entrance to Chesiapeake 

 bay in six weeks. Prof. A. E. Verrill writes that " T. navalis is very abundant and 

 destructive on the southern coast of New England. At my summer home on an island 

 near New Haven it will reduce 2-inoh planks and 4-inch stakes to a honeycomb con- 

 dition in one season — 1st July to September — as I have often proved by experience."^ 

 Although only a very thin film of wood separates the innumerable burrows, they in 

 no case intersect or cut into each other. 



The time of year at which timber is cut, according to Mr. Miller, is an important 

 factor in determining the extent to which it is subject to or immune from the ravages 

 of the Teredo. " Trees cut during the months from October to January give much 

 greater resistance or are less attractive to the Teredo than the trees cut from February 

 to May. The Teredo is practically inactive during the cold of winter." 



One of the peculiarities of the boring habits of Teredo is its aversion to boring 

 from one timber to another, no matter how firmly attached and adjusted they may be. 

 " Over a shipbuilding experience of fifty years our general foreman of works, Mr. 

 John White, observed only two cases where worms had worked from the hull planking 

 into the timbers of vessels. 



" Spawning time appears to be about July, Vessels launched in spring and 

 hauled out before July, and those launched in October are practically free of the 

 Teredo; those exposed during the latter part of June and during July, if not pro- 

 tected, being very freely attacked." 



" To a great extent the Teredo will attack improtected vessel hulls as freely as 

 fixed timber, particularly if remaining idle for any length of time. Constant motion 

 through the water, however, appears to hamper the attachment of the spawn to some 

 little extent. Such protection, however, as tarring, copper or marine painting and 

 creosoting proves an effective measure as long as the protecting agent remains intact." 



" The point of entry of the borer spawn into the timber is below half -tide mark. 

 A peculiarity is that standing timbers show a severed condition (very much after the 

 fashion produced by the beaver), at from one to two feet above low-water spring tide 

 mark in localities where spring tide's have a range of 9 to 11 feet. From this point 

 down the borers work entirely within the timber, not passing the line of the bottom, 

 where this is muddy, but not having the same objection to sand, as shown by the 

 specimen forwarded." 



" Mr. Crandall, of the Crandall Engineering Concern, Boston, Mass., has made 

 the statement to me, that if timber could be kept covered with a film of mud, it would 

 be kept immune through the entry of Teredo spawn being prevented. Certain it is, that 

 all other things being equal (particularly temperature and saltiness) the Teredo is 

 much more prevalent and destructive where the surrounding shore and bottom is sandy. 

 In twenty years' experience this office has never observed a creosoted stick affected 

 by the Teredo. The impregnation used is fourteen and sixteen pounds to the cubic 

 foot."4 



A small amount of creosote appears to be not very effective, since Stearns states 

 that at Christiania, where the Teredo is very destructive, he was told that " all the 



iProc. and Trans. N.S., Inst. Nat. Sci., Vol. V, 1881, p. 365. 



2 Stearns, R. E. C. — The Teredo or Ship-worm. American Naturalist, Vol. XX, 1886, pp. 

 134-135. 



3 Verrill, A, E. Letter to the author, February 21. 1917. 



4 Letter from H. E. Miller, to the author. 



