See that catbird, all lead-color, with a black cap. See her dodge into that bush just beyond us. It is just the place for her nest; and, sure enough, here it is. It is a rough affair, but she mews as pitifully at us as if it were the finest of homes, and half a dozen other birds are already screaming their sympathy. Let us just look at the eggs, and remember that they are a deep polished green, and then walk on, for the poor mother is very unhappy. We have no use for the eggs, and it would be shameful to rob her; and, besides, we should thus destroy the coming lives of four catbirds, who will be too useful as insect-hunters in our gardens to be wasted.
This path is dusty, and we notice a great many pinhole doors of the little black ants. The ants are running in and out of them, and if we should carefully dig up the ground we would find a labyrinth of narrow passages, here and there widening into chambers, and so learn that these tiny holes are entrances to an ant-city whose streets are all subways.
Here are some larger ants—three times as big—a regular procession of them going and coming out from under that half-buried stone, winding through the grass, and then trotting up and down this tree-trunk. A lot of them go out along that low limb. Let us climb upon the fence, and try to see what it is that attracts them. Ah! This is the secret. Clustered thickly on the bark are hundreds of minute green creatures, smaller than pinheads. They are busily sucking the sap from the bark, and seem to interest the ants greatly, for they are stroking these bark-lice (aphids) with their feelers, and if we had a magnifying-glass we could see that they were licking up a honey-like liquid which oozes out of two short tubes on the back of each aphid.
A little distance beyond the ant's apple-tree a young maple stretches one of its branches out to the sunlight just above our heads, where the sharp eyes which young naturalists must keep wide open when they walk abroad will notice a bird's nest hung under the shelter of its broad outermost leaves. It is one of the loveliest nests in the world. A slim, graceful, olive-green little bird glides out from beneath the maple-leaves as we approach, perches near by and watches us silently. Though she does not mew and scream as did the catbird, she is just as anxious, you may be sure. Be easy, dear little vireo—for we know your name—we shall not ruin your home. Let us pull the branch gently down a little. Now we can see that the nest is a round hammock, woven of grapevine bark and spider-web, and hung by its edges. It seems too fragile to hold the weight of the mother, slight as she is; and in it are three white eggs with a circle of pink and purple dots around their larger ends. But here is also a fourth egg, much larger, grayish white, and speckled all over with brown.
That is the egg of the cowbird, a sort of purple, brown-headed blackbird which you may almost always see in pastures where there are cattle. The cowbirds, like the European cuckoos, never build any nests of their own, but put their eggs into those of other birds, and leave them to be hatched. And they are very fond of choosing the nest of a vireo. One would think that the mother would notice at once that a strange egg had been placed in her nest, and would throw it out. But she never seems to do so, but sits on the cowbird egg as well as on her own, so that in course of time she hatches out three or four little vireos and one young cowbird. Then what do you think the stranger does? Why, as soon as the mother vireo goes out to look for caterpillars for food, it begins to wriggle underneath the other little birds, and soon shoves them out of the nest, one after another. Still more strange is it, that when the vireo comes back she never seems to care that her own little ones are all lying dead on the ground below, but gives all the food that they would have eaten to the cowbird. And the greedy cowbird eats it all! Until it is fledged she feeds it in this way, and takes the greatest care of it, and even after it has left the nest and is able to fly about she will come and put caterpillars into its beak.
Look at the trunk of this tree. Why has so much of the bark fallen away from the wood? And what is this curious pattern engraved, as it were, upon the wood—a broad groove running downward, and a number of smaller grooves branching out from this on each side?
Ah! that is the work of a very odd little beetle, with a black head and reddish-brown wing-cases. About eighteen months ago, probably, a mother beetle came flying along, settled on the tree, and bored a hole through the bark, just big enough for her to pass through. Then she began to burrow downward between the bark and the wood, cutting the central groove which you see in the pattern. As she did so she kept on laying eggs, first on one side of the groove and then on the other, in the short branch-tunnels, which she cut out as she went along. In this way she laid, perhaps, eighty or ninety eggs altogether. When the last had been laid she turned round, climbed up her burrow again, passed into the hole by which she came in, and—died in it! And by so doing she blocked up her burrow with her dead body, and so prevented centipedes and other hungry creatures from getting in and eating up her eggs.
Early in the following spring all the eggs hatched, and out came a number of hungry little grubs with hard, horny heads and strong, sharp little jaws. Every one of these grubs at once began to make a burrow of its own, boring away at right angles to the groove made by the mother beetle, and cutting away the fibers which bind the bark to the wood. The consequence was, of course, that by the time they were fully grown quite a big piece of bark had been cut away. And very likely if we were to come and look at the tree again in two years' time we should find that the whole of the trunk had been completely stripped.
"Then these little beetles are very mischievous?" Oh, no, they are not; for they never touch a healthy tree. They only attack those trees which are sickly or diseased.
Here we are on the banks of the stream. Let us make our way home by the path which lies beside it.