Although the _teredo_ appears to penetrate all kinds of timber, that which it seems to destroy with the greatest ease is fir, in which it works much more speedily and successfully than in any other, and perhaps grows to the greatest size. In a fir pile, taken from the old pier-head at Southend, a worm was found 2 feet long and ¾ inch in diameter, and indeed they have been heard of 3 feet in length and 1 inch in diameter. The soft, porous nature of the wood is no doubt the cause of their rapid growth, for in oak timber they do not progress so fast, or grow to so great a length, though in Sir Hans Sloane’s ‘History of Jamaica’ (1725) there are accounts of these animals destroying keels of ships made of oak, and even of cedar, although the latter is renowned, by its smell and resin, for resisting all kinds of worms. [Illustration: _Shell left by the Teredo Navalis._ _Cell formed by the Teredo Navalis showing method of boring._] There is another kind of worm which is very destructive to timber, which Smeaton observed in Bridlington piers. This is the TIMBER-BORING SHRIMP, or GRIBBLE, the _Limnoria terebrans_ (or _Limnoria perforata_, Leach), a mollusc of the family _Asselotes_, Leach. The _Limnoria terebrans_ is very abundant around the British shores. Its ravages were first particularly observed in the year 1810, by the late Sir. Robert Stevenson, engineer of the Bell Rock Lighthouse. While engaged in the erection of that structure he found the timber of the temporary erections to be soon destroyed by the attacks of the _limnoria_. So little was known of the _limnoria_ at the time that Dr. Leach, a well-known naturalist, who received some specimens from Mr. Stevenson, in 1811, declared it to be a new and highly interesting species. In 1834, the late Dr. John Coldstream wrote a very full and interesting description of the creature. The _limnoria_ resembles a woodlouse, and is so small as hardly to be perceptible in the timber it attacks, being almost of the same colour. Small as is this crustacean, hardly larger indeed than a grain of rice, it is a sad pest wherever submarine timber is employed, for it works with great energy, and its vast numbers quite compensate for the small size of each individual; for as many as twenty thousand will appear on the surface of a piece of a pile only 12 inches square. It proceeds in a very methodical manner, and makes its way obliquely inward, unless it happens to meet a knot, when it passes round the obstacle and resumes its former direction. The surface of the timber being first attacked, it proceeds progressively into the wood to the depth of about 1½ inch: the tunnels being cylindrical, perfectly smooth winding holes, about ⅟16th inch in diameter: it is necessary that the holes should be filled with salt water. The outward crust formed by these attacks then becomes macerated and rotten, and is gradually washed away by the beating of the sea. The _limnoria_ does not work by means of any tool or