cluding birds, because their number and ability to consume remains practically a fixed quantity due to their slow rate of multiplication. It sounds large when we find 100 larvae of an elm-leaf beetle in a bird stomach and find 100 birds to an acre; but when we find 100 larvae on a dozen leaves and many thousands of leaves on a tree, the figures lose in impressiveness." Birds eat parasitized forms as well as healthy. The wood-leopard moth is injurious only in cities where the English sparrow keeps out other birds, though the writer thinks the sparrow did destroy the span-worm.27 No further argument would seem to be necessary to show that man must not carelessly upset this delicate balance of nature. This is not to be taken as an argument against such an upset for there can be no development without it. It merely means that man must count the cost. Even where the change made is clearly for man's benefit, the results have always been uniformly satisfactory. In Montana I have seen acres of grain cut close to the ground by the prairie dogs, which were as fat as the ordinary pug dog. The new food supply had just met their taste and they reaped in advance of the farmer. The Department of Agriculture stated some years ago that the increase of these animals in parts of Kansas was an actual threat to the human population. In parts of California rabbits commit similar depredations, and great hunts are often organized to reduce their numbers. Whenever man interferes in this great chain of interrelated forms of life, he runs great risk of producing the most unexpected results. Today in civilized lands few matters are more closely regulated than the importation 27 SMITH, J. B. o. c., p. 136 ff. of strange forms of life, and the bringing in of those likely in any way to cause trouble is strictly prohibited. This is the result of experience. To be sure all our domestic animals have been brought here. Unfortunately all our importations have not been so happy. Go where you will in the East today and the old, neglected apple orchards are full of dead limbs. Examine the twigs and if not too long dead they will look as if there had been some eruption on the bark. In orchards properly cared for once or twice a year the trees are all sprayed with some oil or salt and sulphur solution. Years ago there came in on fruit stock from Asia what we now call the San José scale. It is a minute shield protecting a tiny body fastened to the bark as by a pin. Yet this insignificant scale increases so rapidly and is spread so fast by birds that in a generation the country is practically covered. It was spread in a measure also by the nurseries which scattered infected stock ere its significance was known. Attacking a large share of our prized fruit trees it imposes a burden of care and expense that is enormous, or else destroys our fruit. We are encouraged by the fact that the scale has been attacked by a parasite which has destroyed it in some districts. In 1868 or 1869 a French entomologist near Boston was experimenting with gypsy moths hoping to find a cocoon of commercial value. A storm set some of the moths free. The anxiety of the student to recover the specimens was ridiculed. Down to 1912 the government and the New England States had spent some $7,680,000 in the effort to get rid of them and no New Englander treats the subject as a joke, though I am told that the canny inspectors are careful to miss enough nests to make sure of their jobs the next season. About the first of August the wingless female gypsy moth crawls to some sheltered spot on a tree and lays masses of perhaps 250 eggs each. These hatch out the next May and the young begin to eat the leaves. As if this were not enough the brown-tailed moth has appeared. These may often be seen in great pasty white masses covering electric poles, wires and globes in the evenings. In July the female lays her eggs on some leaf. These hatch in a few days and feeding begins. Then a winter nest is made of leaves which remain decorating the tips of the branches till spring. From scattered spots on the Maine coast down to Fall River and west to the Berkshires these enemies of foliage have spread. If the shade trees are to be saved a constant warfare must be waged. The European house sparrow known to us as the English sparrow was introduced by would-be public benefactors. As Hornaday says, "It is a national sorrow almost too great to be endured." 28 So far as we can see it is a quarrelsome, noisy, dirty bird which has driven out of the towns many desirable native species. It prefers grain to weeds and its board bill is large. On one occasion I saw it eating brown-tailed moths and I hope against hope that this may become a habit. The bird was introduced into America in 1850 by the directors of the Brooklyn Institute. In the next decade it appeared in a number of places in the country, having been brought over apparently by Europeans who missed it. It was likewise taken to Australia and has given the same trouble there. The European starling, another bird of doubtful virtue first liberated in Central Park, New York City, in 1890, has now spread from Massachusetts to Virginia and may 28 HORNADAY, W. T. o. c., p. 334. become a serious menace to the fruit industry as it has in Australia. The English introduced the rabbit into Australia about 1860. The results were astounding; grass, bark of trees, fruit and vegetables were consumed. "In order to protect such portions of the country as are still free from rabbits, fences of wire netting have been erected; one of these fences erected by the government of Victoria extending for a distance of upwards of one hundred and fifty geographical miles. In New Zealand, where the rabbit has been introduced little more than twenty years, its increase has been so enormous, and the destruction it inflicts so great, that in some districts it has actually been a question whether colonists should not vacate the country rather than attempt to fight against the plague. The average number of rabbit skins exported annually from New Zealand is now twelve millions." 29 In 1872 the mongoose, which in its Indian home feeds on rats and snakes, was introduced into Barbados and Jamaica to get rid of the rats which were injuring the cane fields. The attempt was only too successful. The rats gone, birds and chickens were attacked; even the cane has been attacked, and everywhere the mongoose is a scourge. Now we are told that owing to the absence of the birds Jamaica is having trouble with ticks introduced from Mexico. The mongoose has reached many other islands of the Caribbean and Hawaii. "The progress of the pest is everywhere the same,- sweeping destruction of rats, snakes, wild birds, small mammals and finally poultry and vegetables." 30 If it ever gets loose in this 29 HORNADAY, W. T. o. c., p. 331. 30 Ibid., p. 333. country it will be a serious matter. It is claimed that Florida is having increased difficulty from moccasins and muskrats because of the killing of the alligators. In like unconscious fashion the insect phylloxera, was introduced from America into France and nearly destroyed the vine culture. The American grape vines when attacked threw out new root shoots but the European vines did not, hence were killed. The Colorado beetle has made its way across the continent in three years, and even to Ireland. The Hessian fly, the Argentine ant, the horn fly, the wood leopard moth and the elm-leaf beetle are other undesirable immigrants. In a word, some of our greatest burdens have been brought upon us by our ignorant or careless upset of nature's balance. In earlier times man did relatively little harm to those forms of life on which he most directly depended. This was due in part to a lack of death-dealing weapons; in part to the absence of the philosophy expressed in what has been considered a characteristic English fashion: "It's a fine day-let's go and kill something." The ruthless slaughter of the last three centuries has worked irreparable damage in many ways. There are many signs that man is coming to realize that he is not free to lord it over nature and wantonly destroy her lowlier forms unless he wishes at the same time to make his own life more difficult, perhaps impossible. The recognition that he is a part of nature is bound to change his attitude. Instead of trying to catalogue plants and animals either as friends or enemies he begins to see that each plays some part in the whole cycle. Some he must destroy lest they destroy him. Many more he must protect even though they do him some small harm because of the infinite services they |