DESTRUCTIVE LIFE.
THE engineers in charge of a telegraph-line at Hong- kong were surprised recently by the discovery that about seven miles of their cable, though it was well protected and laid underground in a concrete trough, had been severely damaged. For the greater part of the length oval boles had been bored quite through the casing, down to the copper wire itself. The holes were not caused by chemical action, because they were bored very neatly through no less than six layers of different wrappings, including one-eighteenth of an inch of lead. Though no insects were found, it was agreed that insects must have been the authors of the mischief, though what kind of insects was not obvious. It might be possible to find one which enjoys perforating lead. But these insects seemed to have drilled the holes, not in order to make a passage, but by way of making a meal ! They had taken a dinner of six courses, consisting first of tarred rope, then of lead, then of twisted rope, then of tape, then of hemp fibre, and lastly of indiarubber. The oopper strand had been too much for them. Portions of the damaged cable were sent to the Natural History Museum with a hope that some opinion might be given. The request was complied with as kindly as such requests always are by the various departments there, and the oracle replied that there could be very little doubt that the damage was caused by white ants. Specimens of their peculiar forms of appetite and industry are kept in the Museum, which show not only that they will eat lead, but will also bore through hard sandstone rock. Mr. Drummond, whose theory of the great part played by white ants in the natural economy
of the tropics is well known, says of their obvious and primary, or merely destructive, powers :—" You build your house, and for months fancy that you have pitched upon the one solitary site in the country where there are no white ants. But one day suddenly the door-post totters, and lintel and rafters come down together with a crash. You look at a section of the wrecked timbers, and discover that the whole of the inside is eaten away. The apparently solid logs of which the rest of the house is built are now mere cylinders of bark, and through the thickest of them you could push your finger."
While in the tropics the white ant pulverises every- thing in which the sap of life is not running on earth, the rock-boring and wood-boring shell-fish are among the greatest natural agents of destruction in the shallow waters of the sea. It was not until the builders of iron ships launched the present navies of peace or war upon the deep that the bulls of vessels moored for any time in harbour were safe from their attacks. If Rozhdestvensky's fleet had lain for months in Nossi Be a century ago, the timbers would have been perforated by the ship-boring teredo, as well as draped with weed and barnacles. The shells of these molluscs are elegant and beautiful. They are often not at all obviously adapted for boring. Frequently they are very thin, looking almost like hardened paper. Yet they bore through teak or oak, hardened clay, chalk, rock, and concrete breakwaters, and soon reduce the huge Memel logs that support piers and jetties to mere carious shells, which break up and crumble without warning. On the beach to the west of Worthing masses of chalk rock may be found riddled with the holes made by the pholas shells. In many the shell itself, thin but hard, and. with edges like sharp steel files, remains, either whole or broken, though the creature which dwelt in it has been dead for years. A specimen of fossil wood now before the writer has been perforated in all directions by prehistoric teredos. In a portion only five inches high there must be seventy holes at least, of the size of a penholder. In some the shelly tube has been replaced by spar ; in others the complete cast of the hole is made in spar, hollow in some, solid in others. Most of the teredos have followed the grain of the wood ; others have eaten crossways.
The creature is believed by some to penetrate the wood of ships or piles when very small, and being armed with a cutting screw at the end pointing inwards, bores deeper and wider continually as it goes into the heart of the timber ; it lines the auger-hole which it makes with a kind of shell. Through this tunnel it sucks in the water containing the animaleulae on which it lives, though it is believed also to digest the wood. The only proper shell is the boring apparatus on the animal's bead. Ancient naturalists gave to the creature the significant name of Calamitas narium, the "evil genius of ships." It is said that one form of teredo was brought to British seas in ships from abroad. But there is a native species very little inferior to it in powers of mischief, the ordinary Teredo navalis. It was this which nearly flooded Holland by destroying the main sea-gates of the dykes, and which destroyed solid piles of oak in Plymouth Harbour in five years. A log of deal has been found com- pletely honeycombed in the course of forty days. The teredo always attacks wood either floating on the water or below water. Sheathing with copper, or in the case of piles studding all over with iron nails, which rust and form an armour-coating, is the best protection.
In wet and temperate countries rain and rot clear away the debris of forests, while worms pulverise the moist soil. Con- sequently there is no need for annihilating insects such as the white ant. The most powerful and mischievous boring insect in the inland districts of this country is the caterpillar of the goat moth. The moth itself is one of the largest. The full- grown caterpillar, of a dark flushed red, and covered with shiny plates of horn, is sometimes four and a half inches long. It has 3.n abominable smell, and is unpleasant to every sense. For three years after its emergence from the minute egg, like a seed pearl, the caterpillar lives in and by the wood of the tree which it haunts, working in the very vitals of the wood, and never approaching the bark or perforating the final hole of exit till it is ready to change its state and to turn into a chrysalis. During the last year of its life the boles made are large enough to push an ordinary pencil into, though they are flattened and not round. There may be from five to forty or mare inside the same tree, and this tree a perfectly sound one before the creatures set to work mining it. Soon it begins to show signs of being sick. The leaves turn yellow and drop off, and sap exudes from the escape-holes made by the cater- pillars which matured earliest. Poplar and willow are the favourite food-trees of this caterpillar, though they will attack oak. The writer has seen an oak, not less than a century old, almost killed by them. The holes of exit, about thirty in number, were all close together on a surface which a pocket-handkerchief could cover. When they were made is not known, but the tree has been dying gradually for twenty years, and now is almost leafless. In Kensington some healthy poplar trees planted only twenty years ago were found to be infested with the caterpillars, and soon died. Of late years good large willow trees have become very valuable, as they are in great demand for cricket bats. The almost universal habit of pollarding willows greatly reduces the number fit for this purpose, as the grain must be straight and the wood soft. Timber merchants or cabinetmakers need to be extremely careful in buying a promising-looking tree. Often it is perfectly useless owing to the presence of goat-moth caterpillars in the interior. A few years ago an estate in Suffolk which had been many years in possession of the same family was sold, and part of the timber was disposed of separately. In one meadow were two famous old pollard oaks of peculiar growth, for which a London cabinetmaker paid a considerable sum to cut up into "
curly" oak veneer. One of the trees was found to be riddled by the goat-moth larvae, and useless for any purpose.
Contrasting the time taken by inanimate agents, such as chemical action, moisture, frost, and rain, to destroy organic or inorganic matter, the superior efficiency of destructive life is very remarkable. Only give the pair of jaws or the teredo-mollusc's diamond drill life, and it works at a pace which is simply incredible to accomplish its part in the world's economy. The white ants will cousunie the whole interior of a great timber tree in a few months' work in an African forest, and leave nothing but its cast, made of the mud with which they cover it by night to exclude the light should they perforate its sides. In an English wood a fallen oak would lie for fifty years or a century before it was disintegrated. There are kinds of wood, such as the beech, which will hardly rot in water at all if left to themselves. But the teredo will destroy fibre and substance in forty days. Given the fact that in the general course of Nature rapid dis- solution is desirable after vitality has ceased, these animal destructors seem wonderfully adapted for their part.
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