Chapter XIII: Introduction: Of Birds (2)

The general tendency of man's encroachments upon spontaneous nature has been to increase insect life at the expense of vegetation and of the smaller quadrupeds and birds. Doubtless there are insects in all woods, but in temperate climates they are comparatively few and harmless, and the most numerous tribes which breed in the forest, or rather in its waters, and indeed in all solitudes, are those which little injure vegetation, such as mosquitoes, gnats, and the like. With the cultivated plants of man come the myriad tribes which feed or breed upon them, and agriculture not only introduces new speciss, but so multiplies the number of individuals as to defy calculation. Newly introduced vegetables frequently escape for years the insect plagues which had infested them in their native habitat; but the importation of other varieties of the plant, the exchange of seed, or some more accident, is sure in the long run to carry the egg, the larva, or the chrysalis to the most distant shores where the plant assigned to it by nature as its possession has preceded it. For many years after the colonization of the United States, few or none of the insects which attack wheat in its different stages of growth, were known in America. During the Revolutionary war, the Hessian fly, Cecidomyia destructrix, made its appearance, and it was so called because it was first observed in the year when the Hessian troops were brought over, and was popularly supposed to have been accidentally imported by those unwelcome strangers. Other destroyers of cereal grains have since found their way across the Atlantic, and a noxious European aphis has first attacked the American wheatfields within the last fifteen years. Unhappily, in these cases of migration, the natural corrective of excessive multiplication, the parasitic or voracious enemy of the noxious insect, does not always accompany the wanderings of its prey, and the bane long precedes the antidote. Hence, in the United States, the ravages of imported insects injurious to cultivated crops, not being checked by the counteracting influences which nature had provided to limit their devastations in the Old World, are more destructive than in Europe. It is not known that the wheat midge is preyed upon in America by any other insect, and in seasons favorable to it, it multiplies to a degree which would prove almost fatal to the entire harvest, were it not that, in the great territorial extent of the United States, there is room for such differences of soil and climate as, in a given year, to present in one State all the conditions favorable to the increase of a particular insect, while in another, the natural influences are hostile to it. The only apparent remedy for this evil is, to balance the disproportionate development of noxious foreign species by bringing from their native country the tribes which prey upon them. This, it seems, has been attempted. The United States Census Report for 1860, p. 82, states that the New York Agricultural Society "has introduced into this country from abroad certain parasites which Providence has created to counteract the destructive powers of some of these depredators." [Footnote: On parasitic and entomophagous insects, see a paper by Rondani referred to p. 119 ante.]

This is, however, not the only purpose for which man has designedly introduced foreign forms of insect life. The eggs of the silkworm are known to have been brought from the farther East to Europe in the sixth century, and new silk-spinners which feed on the castor-oil bean and the ailanthus, have recently been reared in France and in South America with promising success. [Footnote: The silkworm which feeds on the ailanthus has naturalized itself in the United States, but also the promises of its utility have not been realized.] The cochineal, long regularly bred in aboriginal America, has been transplanted to Spain, and both the kermes insect and the cantharides have been transferred to other climates than their own. The honey--bee must be ranked next to the silkworm in economical importance. This useful creature was carried to the United States by European colonists, in the latter part of theseventeenth century; it did not cross the Mississippi till the close of the eighteenth, and it is only in 1853 that it was transported to California, where it was previously unknown. The Italian bee, which seldom stings, has lately been introduced into the United States. [Footnote: Bee husbandry, now very general in Switzerland and other Alpine regions, was formerly an important branch of industry in Italy. It has lately been revived and is now extensively prosecuted it that country. It is interesting to observe that many of the methods recently introduced into this art in England and United States, such for example as the removable honey--boxes, are reinventions of Italian systeams at least three hundred years old. See Gallo, Le Venti Giornate dell' Agricultura, cap. XV. The temporary decline of this industry in Italy was doubtless in great measure due to the use of sugar which had taken the place of honed, but perhaps also in part to the decrease of the wild vegetation from which the bee draws more or less of his nutriment. A new was-producing insect, a species of coccus, very abundant in China, where its annual produce is said to amount to the value of ten millions of francs, has recently attracted notice in France. The wax is white, resembling spermaceti, and is said to be superior to that of the bee.]

The insects and worms intentionally transplanted by man bear but a small portion to those accidentally introduced by him. Plants and animals often carry their parasites with them, and the traffic of commercial countries, which exchange their products with every zone and every stage of social existence, cannot fail to transfer in both directions the minute organisms that are, in one way or another associated with almost every object important to the material interests of man. [Footnote: A few years ago, a laborer, employed at a North American port in discharging a cargo of hides from the opposite extremity of the continent, was fatally poisoned by the bite or the sting of an unknown insect, which ran out from a hide he was handling.

The Phylloxera vastatrix, the most destructive pest which has ever attacked European vineyards--for its ravages are fatal not merely to the fruit, but to the vine itself--in said by many entomologists to be of American origin, but I have seen no account of the mode of its introduction.]

The tenacity of life possessed by many insects, their prodigious fecundity, the length of time they often remain in the different phases of their existence, [Footnote: In many insects, some of the stages of life regularly continue for several years, and they may, under peculiar circumstances, be almost indefinitely prolonged. Dr. Dwight mentions the following remarkable case of this sort: "I saw here an insect, about an inch in length, of a brown color tinged with orange, with two antennae, not unlike a rosebug. This insect came out of a tea-table made of the boards of an apple-tree." Dr. Dwight found the "cavity whence the insect had emerged into the light," to be "about two inches in length. Between the hole, and the outside of the leaf of the table, there were forty grains of the wood." It was supposed that the sawyer and the cabinet-maker must have removed at least thirteen grains more, and the table had been in the possession of its proprietor for twenty years.] the security of the retreats into which their small dimensions enable them to retire, are all circumstances very favorable not only to the perpetuity of their species, but to their transportation to distant climates and their multiplication in their new homes. The teredo, so destructive to shipping, has been carried by the vessels whose wooden walls it mines to almost every part of the globe. The termite, or white ant, is said to have been brought to Rochefort by the commerce of that port a hundred years ago. [Footnote: It does not appear to be quite settled whether the termites of France are indigenous or imported. See Quatrefaces, Souvenirs d'un naturaliste, ii., pp. 400, 542, 543.

The white ant has lately appeared at St. Helena and is in a high degree destructive, no wood but teak, and even that not always, resisting it.--Nature for March 2d, 1871, p. 362.] This creature is more injurious to wooden structures and implements than any other known insect. It eats out almost the entire substance of the wood, leaving only thin partitions between the galleries it excavates in it; but as it never gnaws through the surface to the air, a stick of timber may be almost wholly consumed without showing any external sign of the damage it has sustained. The termite is found also in other parts of France, and particularly at Rochelle, where, thus far, its ravages are confined to a single quarter of the city. A borer, of similar habits, is not uncommon in Italy, and you may see in that country handsome chairs and other furniture which have been reduced by this insect to a framework of powder of post, covered, and apparently held together, by nothing but the varnish.

DESTRUCTION OF INSECTS.

It is well known to naturalists, but less familiarly to common observers, that the aquatic larvae of some insects which in other stages of their existence inhabit the land, constitute, at certain seasons, a large part of the food of fresh-water fish, while other larvae, in their turn, prey upon the spawn and even the young of their persecutors. [Footnote: I have seen the larva of the dragon-fly in an aquarium bite off the head of a young fish as long as itself.] The larvae of the mosquito and the gnat are the favorite food of the trout in the wooded regions where those insects abound. [Footnote: Insects and fish--which prey upon and feed each other--are the only forms of animal life that are numerous in the native woods, and their range is, of course, limited by the extent of the waters. The great abundance of the trout, and of other more or less allied genera in the lakes of Lapland, seems to be due to the supply of food provided for them by the swarms of insects which in the larva state inhabit the waters, or, in other stages of their life, are accidentally swept into them. All travellers in the north of Europe speak of the gnat and the mosquito as very serious drawbacks upon the enjoyments of the summer tourist, who visits the head of the Gulf of Bothnia to see the midnight sun, and the brothers Laestadius regard them as one of the great plagues of sub-arctic life. "The persecutions of these insects," says Lars Levi Laestadius [Culex pipiens, Culex reptans, and Culex pulicaris], "leave not a moment's peace, by day or night, to any living creature. Not only man, but cattle, and even birds and wild beasts, suffer intolerably from their bite." He adds in a note, "I will not affirm that they have ever devoured a living man, but many young cattle, such as lambs and calves, have been worried out of their lives by them. All the people of Lapland declare that young birds are killed by them, and this is not improbable, for birds are scarce after seasons when the midge, the gnlat, and the mosquito are numerous."--Om Uppodlingar i Lappmarken, p. 50.

Petrus Laestadius makes similar statements in his Journal for forsta urst, p. 283.]

Earlier in the year the trout feeds on the larvae of the May fly, which is itself very destructive to the spawn of the salmon, and hence, by a sort of house-that-Jack-built, the destruction of the mosquito, that feeds the trout that preys on the May fly that destroys the eggs that hatch the salmon that pampers the epicure, may occasion a scarcity of this latter fish in waters where he would otherwise be abundant. Thus all nature is linked together by invisible bonds, and every organic creature, however low, however feeble, however dependent, is necessary to the well-being of some other among the myriad forms of life with which the Creator has peopled the earth.

I have said that man has promoted the increase of the insect and the worm, by destroying the bird and the fish which feed upon them. Many insects, in the four different stages of their growth, inhabit in succession the earth, the water, and the air. In each of these elements they have their special enemies, and, deep and dark as are the minute recesses in which they hide themselves, they are pursued to the remotest, obscurest corners by the executioners that nature has appointed to punish their delinquencies, and furnished with cunning contrivances for ferreting out the offenders and dragging them into the light of day. One tribe of birds, the woodpeckers, seems to depend for subsistence almost wholly on those insects which breed in dead or dying trees, and it is, perhaps, needless to say that the injury these birds do the forest is imaginary. They do not cut holes in the trunk of the tree to prepare a lodgment for a future colony of boring larvae, but to extract the worm which has already begun his mining labors. Hence these birds are not found where the forester removes trees as fast as they become fit habitations for such insects. In clearing new lands in the United States, dead trees, especially of the spike-leaved kinds, too much decayed to serve for timber, and which, in that state, are worth little for fuel, are often allowed to stand until they fall of themselves. Such stubs, as they are popularly called, are filled with borers, and often deeply cut by the woodpeckers, whose strong bills enable them to penetrate to the very heart of the tree and drag out the lurking larvae. After a few years, the stubs fall, or, as wood becomes valuable, are cut and carried off for firewood, and, at the same time, the farmer selects for felling, in the forest he has reserved as a permanent source of supply of fuel and timber, the decaying trees which, like the dead stems in the fields, serve as a home for both the worm and his pursuer. We thus gradually extirpate this tribe of insects, and, with them, the species of birds which subsist principally upon them. Thus the fine, large, red-headed woodpecker, Picus erythrocephalus, formerly very common in New England, has almost entirely disappeared from those States, since the dead trees are gone, and the apples, his favorite vegetable food, are less abundant.

There are even large quadrupeds which feed almost exclusively upon insects. The ant-bear is strong enough to pull down the clay houses built by the species of termites that constitute his ordinary diet, and the curious ai-ai, a climbing quadruped of Madagascar, is provided with a very slender, hook-nailed finger, long enough to reach far into a hole in the trunk of a tree, and extract the worm which bored it. [Footnote: On the destruction of insects by reptiles, see page 125 ante.]

Minute Organisms.

Besides the larger inhabitants of the land and of the sea, the quadrupeds, the reptiles, the birds, the amphibia, the crustacea, the fish, the insects, and the worms, there are other countless forms of vital being. Earth, water, the ducts and fluids of vegetable and of animal life, the very air we breathe, are peopled by minute organisms which perform most important functionsin both the living and the inanimate kingdoms of nature. Of the offices assigned to these creatures, the most familiar to common observation is the extraction of lime, and, more rarely, of silex, from the waters inhabited by them, and the deposit of these minerals in a solid form, either as the material of their habitations or as the exuviae of their bodies. The microscope and other means of scientific observation assure us that the chalk-beds of England and of France, the coral reefs of marine waters in warm climates, vast calcareous and silicious deposits in the sea and in many fresh-water ponds, the common polishing earths and slates, and many species of apparently dense and solid rock, are the work of the humble organisms of which I speak, often, indeed, of animaculae so small as to become visible only by the aid of lenses magnifying thousands of times the linear measures. It is popularly supposed that animalculae, or what are commonly embraced under the vague name of infusoria, inhabit the water alone, but naturalists have long known that the atmospheric dust transported by every wind and deposited by every calm is full of microscopic life or of its relics. The soil on which the city of Berlin stands, contains, at the depth of ten or fifteen feet below the surface, living elaborators of silex; [Footnote: Wittwer, Physikalische Geographie, p. 142.] and a microscopic examination of a handful of earth connected with the material evidences of guilt has enabled the naturalist to point out the very spot where a crime was committed. It has been computed that one-sixth part of the solid matter let fall by great rivers at their outlets consists of still recognizable infusory shells and shields, and, as the friction of rolling water must reduce many of these fragile structures to a state of comminution which even the microscope cannot resolve into distinct particles and identify as relics of animal or of vegetable life, we must conclude that a considerably larger proportion of river deposits is really the product of animalcules. [Footnote: To vary the phrase, I make occasional use of animaloule, which, as a popular designation, embraces all microscopic organisms. The name is founded on the now exploded supposition that all of them are animated, which was the general belief of naturalists when attention was first drawn to them. It was soon discovered that many of them were unquestionably vegetable, and there are numerous genera the true classification of which is a matter of dispute among the ablest observers. There are cases in which objects formerly taken for living animalcules turn out to be products of the decomposition of matter once animated, and it is admitted that neither spontaneous motion nor even apparent irritability are sure signs of animal life.]

It is evident that the chemical, and in many cases mechanical, character of a great number of the objects important in the material economy of human life, must be affected by the presence of so large an organic element in their substance, and it is equally obvious that all agricultural and all industrial operations tend to disturb the natural arrangements of this element, to increase or to diminish the special adaptation of every medium in which it lives to the particular orders of being inhabited by it. The conversion of woodland into pasturage, of pasture into plough land, of swamp or of shallow sea into dry ground, the rotations of cultivated crops, must prove fatal to millions of living things upon every rood of surface thus deranged by man, and must, at the same time, more or less fully compensate this destruction of life by promoting the growth and multiplication of other tribes equally minute in dimensions. I do not know that man has yet endeavored to avail himself, by artificial contrivances, of the agency of these wonderful architects and manufacturers. We are hardly well enough acquainted with their natural economy to devise means to turn their industry to profitable account, and they are in very many cases too slow in producing visible results for an age so impatient as ours. The over-civilization of the nineteenth century cannot wait for wealth to be amassed by infinitesimal gains, and we are in haste to SPECULATE upon the powers of nature, as we do upon objects of bargain and sale in our trafficking one with another. But there are still some cases where the little we know of a life, whose workings are invisible to the naked eye, suggests the possibility of advantageously directing the efforts of troops of artisans that we cannot see. Upon coasts occupied by the corallines, the reef-building animalcule does not work near the mouth of rivers. Hence the change of the outlet of a stream, often a very busy matter, may promote the construction of a barrier to coast navigation at one point, and check the formation of a reef at another, by diverting a current of fresh water from the former and pouring it into the sea at the latter. Cases may probably be found, in tropical seas, where rivers have prevented the working of the coral animalcules in straits separating islands from each other or from the mainland. The diversion of such streams might remove this obstacle, and reefs consequently be formed which should convert an archipelago into a single large island, and finally join that to the neighboring continent. Quatrefages proposed to destroy the teredo in harbors by impregnating the water with a mineral solution fatal to them. Perhaps the labors of the coralline animals might be arrested over a considerable extent of sea-coast by similar means. The reef-builders are leisurely architects, but the precious coral is formed so rapidly that the beds may be refished advantageously as often as once in ten years. [Footnote: The smallest twig of the precious coral thrown back into the sea attaches itself to the bottom or a rock, and grows as well as on its native stem. See an interesting report on the coral fishery, by Sant' Agabio, Italian Consul-General at Algiers, in the Bollettino Consolare, published by the Department of Foreign Affairs, 1862, pp. 139, 151, and in the Annali di Agricoltura Industria e Commercio, No. ii., pp. 300, 373.]

It does not seem impossible that branches of this coral might be attached to the keel of a ship and transplanted to the American coast, where the Gulf stream would furnish a suitable temperature beyond the climatic limits that otherwise confine its growth; and thus a new source of profit might perhaps be added to the scanty returns of the hardy fisherman. In certain geological formations, the diatomaceae deposit, at the bottom of fresh-water ponds, beds of silicious shields, valuable as a material for a species of very light firebrick, in the manufacture of water-glass and of hydraulic cement, and ultimately, doubtless, in many yet undiscovered industrial processes. An attentive study of the conditions favorable to the propagation of the diatomaceae might perhaps help us to profit directly by the productivity of this organism, and, at the same time, disclose secrets of nature capable of being turned to valuable account in dealing with silicious rocks, and the metal which is the base of them.

Our acquaintance with the obscure and infinitesimal life of which I have now been treating is very recent, and still very imperfect. We know that it is of vast importance in geology, but we are so ambitious to grasp the great, so little accustomed to occupy ourselves with the minute, that we are not yet prepared to enter seriously upon the question how far we can control and utilize the operations, not of unembodied physical forces merely, but of beings, in popular apprehension, almost as immaterial as they.

Disturbance of Natural Balances.

It is highly probable that the reef-builders and other yet unstudied minute forms of vital existence have other functions in the economy of nature besides aiding in the architecture of the globe, and stand in important relations not only to man but to the plants and the larger sentient creatures over which he has dominion. The diminution or multiplication of these unseen friends or foes may be attended with the gravest consequences to all his material interests, and he is dealing with dangerous weapons whenever he interferes with arrangements pre-established by a power higher than his own. The equation of animal and vegetable life is too complicated a problem for human intelligence to solve, and we can never know how wide a circle of disturbance we produce in the harmonics of nature when we throw the smallest pebble into the ocean of organic being. This much, however, the facts I have hitherto presented authorize us to conclude: as often as we destroy the balance by deranging the original proportions between different orders of spontaneous life, the law of self-preservation requires us to restore the equilibrium, by either directly returning the weight abstracted from one scale, or removing a corresponding quantity from the other. In other words, destruction must be either repaired by reproduction, or compensated by new destruction in an opposite quarter. The parlor aquarium has taught even those to whom it is but an amusing toy, that the balance of animal and vegetable life must be preserved, and that the excess of either is fatal to the other, in the artificial tank as well as in natural waters. A few years ago, the water of the Cochituato aqueduct at Boston became so offensive in smell and taste as to be quite unfit for use. Scientific investigation found the cause in the too scrupulous care with which aquatic vegetation had been excluded from the reservoir, and the consequent death and decay of the animalculae, which could not be shut out, nor live in the water without the vegetable element. [Footnote: It is remarkable that Pulisay, to whose great merits as an acute observer I am happy to have frequent occasion to bear testimony, had noticed that vegetation was necessary to maintain the purity of water in artificial reservoirs, though he mistook the rationale of its influence, which he ascribed to the elemental "salt" supposed by him to play an important part in all the operations of nature. In his treatise upon Waters and Fountains, p. 174, of the reprint of 1844, he says: "And in special, thou shalt note one point, the which is understood of few: that is to say, that the leaves of the trees which fall upon the parterre, and the herbs growing beneath, and singularly the fruits, if any there be upon the trees, being decayed, the waters of the parterre shall draw onto them the salt of the said fruits, leaves, and herbs, the which shall greatly better the water of thy fountains, and hinder the putrefaction thereof."]

Animalcular Life.

Nature has no unit of magnitude by which she measures her works. Man takes his standards of dimension from himself. The hair's breadth was his minimum until the microscope told him that there are animated creatures to which one of the hairs of his head is a larger cylinder than is the trunk of the giant California sequoia to him. He borrows his inch from the breadth of his thumb, his palm and span from the width of his hand and the spread of his fingers, his foot from the length of the organ so named; his cubit is the distance from the tip of his middle finger to his elbow, and his fathom is the space he can measure with his outstretched arms. [Footnote: The French metrical system seems destined to be adopted throughout the civilized world. It is indeed recommended by great advantages, but it is very doubtful whether they are not more than counterbalanced by the selection of too large a unit of measure, and by the inherent intractability of all decimal systems with reference to fractional divisions. The experience of the whole world has established the superior convenience of a smaller unit, such as the braccio, the cubit, the foot, and the palm or span, and in practical life every man finds that he haa much more frequent occasion to use a fraction than a multiple of the metre. Of course, he must constantly employ numbers expressive of several centimetres or millimetres instend of the name of a single smaller unit than the metre. Besides, the metre is not divisible into twelfths, eighths, sixths, or thirds, or the multiples of any of these proportions, two of which at least--the eighth and the third--are of as frequent use as any other fractions. The adoption of a fourth of the earth's circumference as a base for the new measures was itself a departure from the decimal system. Had the Commissioners taken the entire circumference as a base, and divided it into 100,000,000 instead of 10,000,000 parts, we should have had a unit of about sixteen inches, which, as a compromise between the foot and the cubit, would have been much better adapted to universal use than so large a unit as the metre.] To a being who instinctively finds the standard of all magnitudes in his own material frame, all objects exceeding his own dimensions are absolutely great, all falling short of them absolutely small. Hence we habitually regard the whale and the elephant as essentially large and therefore important creatures, the animalcule as an essentially small and therefore unimportant organism. But no geological formation owes its origin to the labors or the remains of the huge mammal, while the animalcule composes, or has furnished, the substance of strata thousands of feet in thickness, and extending, in unbroken beds, over many degrees of terrestrial surface. If man is destined to inhabit the earth much longer, and to advance in natural knowledge with the rapidity which has marked his progress in physical science for the last two or three centuries, he will learn to put a wiser estimate on the works of creation, and will derive not only great instruction from studying the ways of nature in her obscurest, humblest walks, but great material advantage from stimulating her productive energies in provinces of her empire hitherto regarded as forever inaccessible, utterly barren. [Footnote: The fermentation of liquids, and in many cases the decomposition of semi-solids, formerly supposed to be owing purely to chemical action, are now ascribed by many chemists to vital processes of living minute organisms, both vegetable and animal, and consequently to physiological as well as to chemical forces. Even alcohol is stated to be an animal product. The whole subject of animalcular, or rather minute organic, life, has assumed a now and startling importance from the recent researches of naturalists and physiologists, in the agency of such life, vegetable or animal, in exciting and communicating contagious diseases, and it is extremely probable that what are vaguely called germs, to whichever of the organic kingdoms they may be assigned, creatures inhabiting various media, and capable of propagating their kind and rapidly multiplying, are the true seeds of infection and death in the maladies now called zymotic, as well perhaps as in many others.

The literature of this subject is now very voluminous. For observations with high microscopic power on this subject, see Beale, Disease Germs, their supposed Nature, and Disease Germs, their real Nature, both published in London in 1870.

The increased frequency of typhoidal, zymotic, and malarious diseases in some parts of the United States, and the now common occurrence of some of them in districts where they were unknown forty years ago, are startling facts, and it is a very interesting question how far man's acts or neglects may have occasioned the change. See Third Anual Report of Massachusetts State Board of Health for 1873. The causes and remedies of the insalubrity of Rome and its environs have been for some time the object of careful investigation, and many valuable reports have been published on the subject. Among the most recent of these are: Relazione sulle condizioni agrarie ed igieniche della Campagna di Roma, per Raffaele Pareto; Cenni Storici sulla questione dell' Agro Romano di G. Guerzoni; Cenni sulle condizioni Fisico-economiche di Roma per F. Giordano; and a very important paper in the journal Lo Sperimentale for 1870, by Dr. D. Pantaleoni.

There are climates, parts of California, for instance, where the flesh of dead animals, freely exposed, shows no tendency to putrefaction but dries up and may be almost indefinitely preserved in this condition. Is this owing to the absence of destructive animalcular life in such localities, and has man any agency in the introduction and naturalization of these organisms in regions previously not infested by them ]