SOME ANIMAL ENEMIES OF MAN.
It is a somewhat remarkable fact that the domain of human existence is singularly liable to be intruded upon by lower forms of both animal and plant life, which may in some cases inflict injury of great extent upon man’s possessions or even upon his bodily frame. Not so long ago a foreign member of the beetle-fraternity threatened the interests of agriculturists in this country, and caused consternation to prevail throughout the length and breadth of the land. And although the alarm with which the advent of the insect-intruder was hailed has now disappeared, agriculturists would inform us that their especial territory is beset with other insect-enemies which invariably damage their crops, and which in certain seasons cause the disastrous failure of many a thriving field. Witness in proof of this the ravages of the ‘turnip-fly’ and its neighbours, which blight the crops in some districts to an extent which must be seen to be realised. Or take the case of the hop-grower, whose favourable prospects largely depend on the absence of a small species of plant-lice which specially affects these plants, and which in certain seasons may cause, by their enormous increase, the total failure of this important crop. Nor do our insect-foes confine their ravages to growing-crops. When the fruits of the harvest have been duly gathered in and stored within the granary, even there they are attacked by minute pests. Numberless insects—flies, beetles, and other forms—select the granary as a nursery or suitable place for the upbringing of their young; the larvæ or young insects feeding on the grain and destroying large quantities by their increase as well as by their destructive habits. Apart from the domain of agriculture, however, lower forms of animal and plant life powerfully affect man’s estate. The growth and increase of lower plants produce many skin-diseases; and if it be true—already rendered probable—that epidemics are propagated through the agency of living ‘germs’ which increase after the fashion of lower forms of life, then it may be held that we are liable to be attacked on every side by enemies, insignificant as to size, but of incalculable power when their numbers are taken into consideration. Parasites of various kinds ravage man’s flocks and even affect his own health, so that it is perfectly clear that we do not by any means enjoy any immunity whatever from the enemies which living nature in its prolific abundance produces, and which select man and man’s belongings as their lawful spoil.
The animal enemies of man, concerning which we purpose to say a few words in the present paper, belong to a different sphere from that at which we have just glanced. Some of the most powerful marauders upon human territory belong to the Mollusca or group of the true shell-fish, and present themselves as near relations of the oysters, mussels, and their allies. The molluscs which become of interest to man in other than a gastronomic sense, possess, like the famous oyster, a bivalve shell, or one consisting of two halves. In the first of man’s molluscan enemies to which we may direct attention, the shell is of small size, and so far from inclosing the body of the animal, appears to exist merely as an appendage to one extremity, which for want of a better term, we may name the head—although, as every one knows, no distinct head exists in the oyster and its kind. Suppose that from this head-extremity, bearing its two small shells, a long worm-like or tubular body is continued, and we may then form a rough and ready, but correct idea of the appearance of the famous ‘ship-worm’—the Teredo of the naturalist. This animal was first styled the ‘ship-worm’ by Linnæus and his contemporaries; and in truth it resembles a worm much more closely than its shell-fish neighbours. As a worm, indeed, it was at first classified by naturalists. But appearances in zoological science are as deceptive as they are known proverbially to be in common life, and the progress of research afterwards duly discovered beneath the worm-like guise of the teredo, all the characters of a true mollusc. The long body of the mollusc simply consists of the breathing-tubes, by which water is admitted to the gills, being extremely developed, the body proper being represented by the small portion to which the two small shells are attached.
The importance of the ship-worm arises from the use it makes of these apparently insignificant shells as a boring-apparatus; and any sea-side visitor, residing on a coast where an ocean-swell or severe storms strew the shore with drift-wood, has but to use his eyes to assure himself of the extent and perfection of the ship-worm’s labours. Pieces of drift-wood may be seen to be literally riddled by these molluscs, which live in the burrows they thus excavate. Each habitation is further seen to be coated with a limy layer formed by the tubular body, and the boring for the most part is noted to proceed in the direction of the grain of the wood. The little excavator turns aside in its course, however, when it meets with a knot in the wood, and an iron nail appears of all things to be the ship-worm’s greatest obstacle—a fact which has been taken advantage of, as we shall presently see, by way of arresting its work of destruction.
Linnæus long ago designated the ship-worm as the calamitas navium, and although perhaps the expression as applied to ships is somewhat far-fetched—save in the case of broken-down hulks—and utterly inapplicable in this age of iron, there can be little doubt that regarded relatively to wooden piles, piers, and like erections, the ship-worm is unquestionably a calamity personified. So, at anyrate, thought the Dutch in the years 1731-32, when the teredo began to pay attentions of too exclusive a nature to the wooden piles which supported the great earth-works or ‘dikes’ that keep the sea from claiming the United Provinces as its own. A Dutchman has been well said to pay great attention to two things which are euphoniously and shortly expressed by the words ‘dams’ and ‘drams.’ The former keep the sea from invading his territory, and the latter aid in protecting him personally from the effects of the perennial damp amidst which he exists. The ship-worm in the years just mentioned caused terror to prevail through the length and breadth of the Netherlands, through its appearance in large numbers in the wooden piles of the dams or dikes. On these piles the fortunes of Holland may be said to depend; and the foundations of the Dutch empire might therefore be regarded, correctly enough, as having been sapped and threatened by an envious enemy in the shape of a mollusc, and one belonging to by no means the highest group of that division of animals. The alarm spread fast through the Netherlands, and the government was not slow to appreciate the danger, or to offer a reward of large amount for the discovery of any plan which would successfully stay the progress of such dreaded invaders.
Inventors, it might be remarked, are not slow, as a rule, to accept invitations of such generous nature; and if report speaks truly, the office of discriminating between the worthless and feasible projects which were submitted to the Dutch nation on the occasion referred to, could not have proved either an easy or enviable one. Then came the chemists with lotions innumerable, and the inventors of varnishes, paints, and poisons were in a state of hopeful anxiety. But none of these preparations was found to fulfil the required conditions, and the only project which appeared to savour of feasibility was one which was rejected on account of its impracticable nature—namely that of picking the teredos from their burrows like whelks from their shells. The kingdom of Holland thus appeared in a fair way of being undermined by an enemy of infinitely greater power and one less capable of being successfully resisted than the Grand Turk, who once upon a time declared his intention of exterminating the nation with an army whose only weapons were spades and shovels. But after a period of unrestricted labour, the ship-worm ‘turned tail’ on the Netherlands, and disappeared as suddenly as it had appeared, leaving only a few stragglers to mark the vantage-ground.
Though Britain has not suffered from teredo-epidemics in the same measure as Holland, there can be little doubt that the ravages of this mollusc on the timber of our piers and dockyards, cost us a large sum annually. The stoutest oak is riddled through with the same ease displayed in perforating the softer pine; and in some of our seaport towns, especially on the southern coasts, the yearly estimates for repairs of damage done by the ship-worm form no inconsiderable item in the government or local expenditure as the case may be. The most effectual plan for the repression of the teredo and for the prevention of its work of destruction appears to be that of protecting the exposed timber by driving therein short nails with very broad heads. These nails form a kind of armour-casing which is rendered more effective through the chemical action of the water in producing rust.
Some molluscs, near neighbours of the teredo, and which burrow for the most part into stone, but occasionally perforate wood, are those belonging to the Piddock-family—the genera Pholas and Saxicava of the naturalist—celebrated by Pliny of old as phosphorescent animals. The Saxicavæ have somewhat elongated shells, by means of which they burrow in rocks and lie ensconced in their dwelling-places, and whose perforated rock-homes are eagerly sought after by all who delight in forming rockeries in their gardens. These molluscs have ere now caused fears for the safety of Plymouth breakwater, through the persistence with which they excavated their burrows into the substance of the stones. And as has been well pointed out, the destructive action of these molluscs may pave the way for an inroad of the sea; a riddled mass of rock or stone being rendered through their attack liable to disintegration from the action of the waves.
A final example of an animal enemy of man which as regards size is to be deemed insignificant when compared with the teredo, but which nevertheless adds by its destructive work to our annual expenditure, is the little crustacean known as the Limnoria terebrans, or popularly as the wood-boring shrimp or ‘gribble.’ This animal belongs to the group including the familiar ‘Slaters’ or ‘Wood-lice,’ found under stones and in damp situations, and by means of its powerful jaws burrows deeply into wood of all kinds. Occasionally, the ship-worm and gribble have been found at work in the same locality and have committed ravages of great extent; the latter, on account of its small size, being more difficult of detection and eradication than its molluscan neighbour.
The consideration of a subject such as the present, it may lastly be remarked, possesses a phase not without some degree of consolation to minds which, if incapable of seeing ‘good in everything,’ may nevertheless believe in the adjustment and counterbalancing of most of Nature’s operations. The repression of animal life by parasites may in one sense prove a gain to nature at large, viewed from a Malthusian stand-point, although humanly considered, there may be differences of opinion regarding the applicability of the opinion to the case of man. But if the ravages of the teredo and its neighbours on the works of man are to be considered as a veritable affliction, we must not fail to think also of the service these animals render in clearing the ocean of vast masses of drift-wood, which, liberated from the mouths of all the great rivers of the world, would speedily accumulate to check navigation and impede commerce in many quarters of the world. The genius of Brunel, which discerned in the manner of the ship-worm’s burrowing the true method of excavating the tunnel associated with his name, and which thus improved engineering science by a happy thought and observation, may also be regarded as bearing testimony to the consoling fact that there exist few evils which are entirely unmixed with good.