[Sidenote: Insect destructive to Timber.]
So destructive to timber is this small insect, that the Norway logs, laid down to support the temporary railways in 1807, when lifted in 1811, were found to have been reduced by its ravages from 10 inches square to 7 inches, or at the rate of about an inch in the year. The author having had occasion afterwards to examine the timber-bridge of Montrose, found the attacks of this insect upon the wooden piers to be so alarming as to endanger that fabric; and after many trials for the preservation of timber in such situations, the Trustees were ultimately induced to cover the upright beams with sheet-copper. Upon another occasion, when the author was called to inspect the Crinan Canal, he found the gates of the sea-locks so destroyed, chiefly by this little animal, that the locks lost seven feet of their depth of water in the course of the night. It is further remarked, that the deserted cavities, formed by the perforations of the Limnoria, frequently become the residence of larger marine insects, belonging to the Linnæan genus Oniscus.
[Sidenote: Experiments with pieces of timber trenailed to the Rock.]
In the year 1814, with a view to experiment on the effects of these destructive vermes, I fixed down specimens of teak-wood, oak, black birch, Memel and Norway fir timber, on the Bell Rock. The only specimen which remained imperforate till 1820, was the teak-wood. The rest were almost entirely destroyed in the course of two or three years. This may be regarded as a matter of some importance, in a national point of view, in directing the employment of teak-wood for the sea-lock gates of canals and for ship-timbers. From the excellency of the situation of the Bell Rock for such experiments, I have caused another set of timbers to be trenailed to the rock, in a situation where, like the former, they are occasionally uncovered by the water. These last pieces of timber were laid down in the month of October 1821. They are eighteen in number, each measuring 5 inches square, and 30 inches in length; and are of the following kinds, viz. British and American oaks and firs, Memel fir, Scotch elm, beech, sycamore, larch, teak-wood, mahogany, bullet-tree, locust-wood, and blue gum-wood from Van Dieman’s Land.