On a walk through the woods and fields to-day, how seldom do we find a dead insect! When sick and dying, nine out of ten are snapped up by frog, lizard, or bird; the few which die a natural death seeming to disintegrate into mould within a very short space of time. There is, however, one way in which, through the long, long thousands of centuries, insects have been preserved. The spicy resin which flowed from the ancient pines attracted hosts of insects, which, tempted by their hope of food, met their death—caught and slowly but surely enclosed by the viscid sap, each antenna and hair as perfect as when the insect was alive. Thus, in this strangely fortunate way, we may know and study the insects which, millions of years ago, fed on the flowers or bored into the bark of trees. We have found no way to improve on Nature in this respect, for to-day when we desire to mount a specimen permanently for microscopical work, we imbed it in Canada balsam.
If suddenly the earth should be bereft of all trees, there would indeed be consternation and despair among many classes of animals. Although in the sea there are thousands of creatures, which, by their manner of life, are prohibited from ever passing the boundary line between land and water, yet many sea-worms, as for example the teredo, or ship-worm, are especially fashioned for living in and perhaps feeding on wood, in the shape of stray floating trees and branches, the bottoms of ships, and piles of wharves. Of course the two latter are supplied by man, but even before his time, floating trees at sea must have been plentiful enough to supply homes for the whole tribe of these creatures, unless they made their burrows in coral or shells.
The insects whose very existence, in some cases, depends upon trees, are innumerable. What, for example, would become of the larvæ of the cicada, or locust, which, in the cold and darkness of their subterranean life, for seventeen years suck the juicy roots of trees; or the caterpillars of the moths, spinning high their webs among the leaves; or the countless beetles whose grubs bore through and through the trunk their sinuous, sawdusty tunnels; or the ichneumon fly, which with an instrument—surgical needle, file, augur, and scroll saw all in one—deposits, deep below the bark, its eggs in safety? If forced to compete with terrestrial species, the tree spiders and scorpions would quickly become exterminated; while especially adapted arboreal ants would instantly disappear.
We cannot entirely exclude even fishes from our list; as the absence of mangroves would incidentally affect the climbing perch and catfishes! The newts and common toads would be in no wise dismayed by the passing of the trees, but not so certain tadpoles. Those of our ditches, it is true, would live and flourish, but there are, in the world, many curious kinds which hatch and grow up into frogs in curled-up leaves or in damp places in the forks of branches, and which would find themselves homeless without trees. Think, too, of the poor green and brown tree frogs with their sucker feet, compelled always to hop along the ground!
Lizards, from tiny swifts to sixty-inch iguanas, would sorely miss the trees, while the lithe green tree snakes and the tree boas would have to change all their life habits in order to be able to exist. But as for the cold, uncanny turtles and alligators,—what are trees to them!
In the evolution of the birds and other animals, the cry of “excelsior” has been followed literally as well as theoretically and, with a few exceptions, the highest in each class have not only risen above their fellows in intelligence and structure, but have left the earth and climbed or flown to the tree-tops, making these their chief place of abode.
Many of the birds which find their food at sea, or in the waters of stream and lake, repair to the trees for the purpose of building their nests among the branches. Such birds are the pelicans, herons, ibises, and ospreys; while the wood ducks lay their eggs high above the ground in the hollows of trees. Parrots, kingfishers, swifts, and hummingbirds are almost helpless on the ground, their feet being adapted for climbing about the branches, perching on twigs, or clinging to the hollows of trees. Taken as a whole, birds would suffer more than any other class of creatures in a deforested world. The woodpeckers would be without home, food, and resting-place; except, possibly, the flicker, or high-hole, who is either a retrograde or a genius, whichever we may choose to consider him, and could live well enough upon ground ants. But as to his nest—he would have to sharpen his wits still more to solve successfully the question of the woodpecker motto, “What is home without a hollow tree?”
Great gaps would be made in the ranks of the furry creatures—the mammals. Opossums and raccoons would find themselves in an embarrassing position, and as for the sloths, which never descend to earth, depending for protection on their resemblance to leaves and mossy bark, they would be wiped out with one fell swoop. The arboreal squirrels might learn to burrow, as so many of their near relations have done, but their muscles would become cramped from inactivity and their eyes would often strain upward for a glimpse of the beloved branches. The bats might take to caves and the vampires to outhouses and dark crevices in the rocks, but most of the monkeys and apes would soon become extinct, while a chimpanzee or orang-utan would become a cripple, swinging ever painfully along between the knuckles of crutch-like forearms, searching, searching forever for the trees which gave him his form and structure, and without which his life and that of his race must abruptly end.
Leaving the relations which trees hold to the animals about them and the part which they have played in the evolution of life on the earth in past epochs, let us consider some of the more humble trees about us. Not, however, from the standpoint of the technical botanist or the scientific forester, but from the sympathetic point of view of a living fellow form, sharing the same planet, both owing their lives to the same great source of all light and heat, and subject to the same extremes of heat and cold, storm and drought. How wonderful, when we come to think of it, is a tree, to be able to withstand its enemies, elemental and animate, year after year, decade after decade, although fast-rooted to one patch of earth. An animal flees to shelter at the approach of gale or cyclone, or travels far in search of abundant food. Like the giant algæ, ever waving upward from the bed of the sea, which depend on the nourishment of the surrounding waters, so the tree blindly trusts to Nature to minister to its needs, filling its leaves with the light-given greenness, and feeling for nutritious salts with the sensitive tips of its innumerable rootlets.
Darwin has taught us, and truly, that a relentless struggle for existence is ever going on around us, and although this is most evident to our eyes in a terrible death battle between two great beasts of prey, yet it is no less real and intense in the case of the bird pouring forth a beautiful song, or the delicate violet shedding abroad its perfume. To realise the host of enemies ever shadowing the feathered songster and its kind, we have only to remember that though four young birds may be hatched in each of fifty nests, yet of the two hundred nestlings an average often of but one lives to grow to maturity,—to migrate and to return to the region of its birth.