CHAPTER VII.

ON THE PRESERVATION OF WOODEN BRIDGES, JETTIES, PILES, HARBOUR WORKS, ETC., FROM THE RAVAGES OF THE TEREDO NAVALIS AND OTHER SEA-WORMS.

"Perforated sore

And drilled in holes, the solid oak is found

By worms voracious, eaten through and through."

SIR JOHN BARROW.

As the destruction of timber by fungi has been called the vegetable rot, it may not be inappropriate to term the destruction of wood by various worms and insects, the animal rot.

We have four natural enemies to deal with: 1st, the dry rot, that attacks our houses, &c.; 2nd, the worms, or boring animals, which destroy our ships and harbours; 3rd, the rust, that eats our iron; and 4th, the moisture and gases, that destroy our stone.

There are three classes of destructive insects which prey upon timber trees, founded upon the manner in which they carry on their operations-viz. those which feed upon the leaves and tender shoots; those which feed upon the bark and the albumen; and those which feed upon the heartwood.

It is to be observed that some of the insects which feed upon the heart of wood do not cease their ravages upon

the removal of the tree; but that, on the contrary, the Cossus syrex, of our indigenous fauna, and the larvæ of the Callidium bajutum, which are often found in imported timber, continue to devour the wood long after it has been inserted in buildings. There seem to be very few means of defence against this class of destructive agents; and very few trustworthy indications of their existence. or of the extent of the ravages they have committed, are to be discovered externally; and it thus frequently happens that a sound, hearty-looking stick of timber may be so seriously bored by these insects as to be of comparatively little value for building purposes of any description. The soft and tender woods, and such as are of a saccharine nature in their juices, are the most liable to be assailed by worms; those which are bitter are generally, if not invariably, exempt; it is obvious, therefore, that those palatable juices, which are so conducive to their production and propagation, should be got rid of by thorough seasoning, and, if further precaution be necessary, that the infusion of some bitter decoction into the pores of the wood will be an effectual preventive; and for which those woods that are of a regular grain afford sufficient facilities. Ash, if felled when abounding in sap, is very subject to worms; beech, under similar circumstances, is also liable to their attacks; likewise alder and birch; in these woods water seasoning is sometimes found to be a good preventive; the sapwood of oak is also thus improved; the silver fir is subject to them; the sycamore is rather so; alder is said when dry to be very susceptible of engendering them; the cedar, walnut, plane, cypress,

and mahogany are examples of woods which discourage their advances. It has been stated that Robert Stevenson (not the son of the "Father of Railways"), of Edinburgh, at Bell Rock Lighthouse (of which he was engineer), between 1814 and 1843, found that greenheart wood, beef wood, and bullet tree were not perforated by the Teredo navalis, and teak but slightly so. Later experiments show that the "jarrah" of the East, also, is not attacked. Lignum vitæ is said to be exempt. The cost of these woods prevents their general use.

In 1810, Stevenson first noticed the teredo in piles, and specimens of the creatures in wood were sent to Dr. Leach, of the British Museum, in 1811, who examined them, and noticed their peculiarities. Stevenson, settled on Bell Rock during many years (like a new Robinson Crusoe), was enabled to watch the injuries done to the piles by the teredo. With piles which had been subjected to Kyan's process before immersion, the wood was attacked at the end of the twenty-eighth month, and was entirely destroyed in the seventh month of the fifth year. With Payne's, it lasted a year longer.

We can give the names of those who have given much time and attention to this subject. At the bottom of this page a list of works of reference* will be found useful. Messrs. Stevenson (engineer of Bell Rock Lighthouse), Harting (Member of the Academy of Sciences of the

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*See 'Proceedings of the Royal Society of Edinburgh,' v. 7, page 433; 'Tredgold's Carpentry,' by J. T. Hurst, 1871; 'Histoire de l'Acad.,' 1765, page 15; Ann. des Ponts et Chaussées,' v. 15, page 307; 'Mem. sur la Conservation des Bois à la Mer,' 1868, by Forestier; 'Bois de Marine,' by Quatrefages, 1848.

Pays-Bas), de Quatrafages, Deshayes, Caillaut, Hancock, Dagneau, de Gemini, Kater, Crepin (Engineer-in-Chief, of Belgium), and A. Forestier (Engineer-in-Chief of the Bridges, &c., of France).

The termite, or white ant, is the most destructive insect to timber on land, whilst the teredo reigns supreme of sea worms in the sea. The former we shall treat of in our next chapter, the latter we propose considering at some length in this.

The marine worm, of which there are accounts in all parts of the world, has been known, by its effects, for hundreds of years; indeed, Ovid spoke of it nineteen hundred years ago, and it is even mentioned by Homer. Fossil terredines of great antiquity have been found near Southend; also pieces of petrified wood from the greensand, near Lyme and Sidmouth, bored by ancient species of teredo; also from Bath, and from Doulting, near Shepton Mallet, specimens of oolite, with petrified corallines in it, pierced by boring shells.

It is said that this worm is a native of India, and that it was introduced to Holland some 200 years ago, from whence it has spread through the ports of northern Europe.

The Teredo navalis* is very destructive to harbour works and piling. The Southampton water is particularly infested with it; in fact, the teredo is found in every port to which coals are carried south of the Tees; in the Thames, as high up as Gravesend; and northward as far

There are eight kinds of teredines, of which three are to be found in European waters, viz. the Teredo fatalis, Teredo navalis, Teredo bipennata.

as Whitby. It is also found at Ryde, Brighton, and Dover. Traces of the ravages of the Teredo navalis, and of the Limnoria terebrans, have at various periods been found from the north of Scotland and Ireland, on almost every coast, to the Cape of Good Hope and Van Dieman's Land, in the eastern hemisphere; and, in the western hemisphere, from the river St. Lawrence to Staten Island, near Terra del Fuego, almost in the Polar Sea; so that although this maritime scourge is rifest in warm climates, yet cold latitudes are not exempt from it.

At the Crystal Palace, Sydenham, may be seen the destructive Teredo navalis in a bottle, and there may also be seen mahogany perforated by it, and fir piles from Lowestoft Harbour, which were rendered useless by the ravages of the worm and the limnoria three years after they were driven, showing the necessity of defending timber intended for marine construction. A specimen of American oak from the dock gates of Lowestoft Harbour, which had been four years under water, and a part of a fir-pile from the dockyard creek at Sevastopol, also show the destructive powers of the teredo. At the South Kensington and British Museums, London, specimens of this worm may also be seen, as well as pieces of timber perforated by it.

The bottoms of ships, and timbers exposed to the action of the sea, are often destroyed by the teredo.

The gunboats constructed during the Crimean war suffered far more from dry rot and the teredo than the shot and shell of the Russians. One cannot even guess at the mischief perpetrated every year all along our