Part 19

We in a strange country, find our way back home by remembering what we saw on the way out. An ant gets home by following the smell of its outward trail. We recognize our friends by sight, and know them by the way they look. An ant recognizes its friends by touching them with its feelers, as no doubt you have often seen ants do, and so getting the familiar odor, smelling out each other’s claims to acquaintance.

For the feelers or antennae are the ant’s nose. It feels with them, and it also smells. As you can discover by looking at any ant, the antenna is like some whips which have a stiff handle and a long flexible lash fastened to its end. The handle sticks out sidewise, and the lash is jointed so that it can be moved about freely.

Our common brown ant has eleven joints in its whip-lash. With the joint at the tip it smells its nest. With the tenth joint it gets the general odor of the colony to which it belongs. With the ninth, it follows the scent of its own track. With the eighth and seventh, it recognizes the helpless young which are its care. By means of the sixth and fifth, it knows its enemies, the inhabitants of other ant cities with which it is at war. What the remaining four joints next the handle are for, is by no means clear.

An ant, therefore, which has had the outermost joint of its feelers cut off, or has lost them in battle, does not know its own nest. One that has lost the two outermost, does not recognize its fellows when it meets them away from home. One that has lost the outermost three joints, can not smell its own track and so can no longer find its way home. If the seventh and eighth joints are gone, the ant no longer has the slightest interest in the eggs and the helpless young, which before the mutilation it would have fought to the death to defend. Apparently, it no longer knows what they are; like the men who wake up some morning with a little blood clot on the surface of their brains over their left ears, who can see words but not read them, and don’t know what their wives and children are. On the other hand, ants from different nests, which have lost the whole of their antennae down to the fourth joint, live together in perfect peace and harmony. But ants from different nests, deprived of their antennae only as far as the sixth joint, straightway start to fighting like cats and dogs; and never leave off till they are all killed or disabled.

Apparently then, the ant has enemy-smelling spots, and egg-smelling spots, and track-smelling spots, and friend-smelling spots, and nest-smelling spots, strung along in order on the lash-like part of its feelers; so that when one of these sets of spots goes, that particular sort of smell goes with it.

The ant, I say, depends greatly on smell. Probably it never knows any of its fellows, or any of its young, separately as individuals. It only knows that they have a certain familiar smell. At any rate, ants taken from a nest, soaked in water with ants from another nest, till they have taken on the foreign odor, and then returned to their own nest, are promptly set upon and killed as if they were invaders. But ants soaked in water with members of the colony, so that they have the proper colonial smell, are received as brothers.

Each sort of ant has its own peculiar odor, so different from that of other sorts that even the blunt human nose can tell them apart. Each nest of ants, too, has a slightly different smell from that of other nests of the same sort, so that each ant knows its own, tho the differences are too small for us to detect. All the ants of a colony are the children of the single queen, who lays all the eggs for the entire ant city. All the ants of a hill, therefore, instead of looking like their mother, smell like her. Each ant, then, recognizes its own brothers and sisters, its mother, its mother’s sisters, and the children of its mother’s sisters, who are its cousins. All these have the familiar smell, and the ant treats them as friends.

Ants from a related nest whose smell is nearly right, but not quite, are received with suspicion, and not allowed to take any part in the care of the young. Those whose odor is still less familiar are dragged about and roughly handled, but allowed to live. But those whose odor is entirely strange are promptly lynched, and their bodies dragged away to the waste heap.

The odor of the queen ant remains the same thruout life. Consequently, any ant will always recognize its own mother. But the odor of the worker ants changes with age. An ant, brought up in a nest, learns the queen odor, and the general nest odor, and the odor of workers of its own age, and of all younger than itself, and of all older than itself to which it is accustomed. But a young ant taken away from its nest, and kept away for two months, will find that its older sisters have meanwhile taken on a new smell. It treats them therefore as enemies. Yet an ant, once familiar with the odor belonging to any age, will remember it for at least two years.

There are some other peculiar results of the ant’s reliance on its smell. Occasionally, in the fields and woods, one finds what are called mixed nests of ants. Two different sorts of ants, which ordinarily are mortal enemies, springing upon one another and fighting to the death on sight, are found living together in harmony, caring for each other’s young, and in all respects behaving as if they were all of the same sort.

The way these arise is this: Two young queens, of different kinds, starting their new colonies, happen to settle so near together that the young workers mix with one another as soon as they are hatched out. From their infancy, therefore, each sort knows the smell of the other; and being used to it, thinks it quite the right and proper thing. So the ants grow up together, while the odors change so slowly with age that they never seem strange. Indeed, such nests have been made in this way by students of the ways of ants, with as many as ten different sorts in them, all living peacefully together.

When, however, such a nest is separated, and the two sorts of ants kept apart for a few months, the mixed nest cannot be reformed. Each sort of worker ant will recognize and care for the queen of the other sort, and all young of the other sort of all ages up to the time when the nest was split up. These the ant remembers. But all workers older than this have, of course, taken on an unfamiliar smell. The old friends have become enemies, to be slain on sight. So each sort of ant befriends the young of the other, whose smell it recalls, tho it has never known the individuals; while it fights to the death its former friends of its own age, with whom it has been working side by side, but whose odor has become strange.

Evidently then, an ant has no instinctive liking for any particular smell. It simply has to learn a set of smells, and what they mean, just as we have to learn our lessons. I think you will agree that for ants living under ground, smell is on the whole the best sense to tie to and do one’s thinking with. But for us, living upstairs in the sunlight, sight is, I am sure, very much the most useful of all the senses.

XXXI

Some Other Eyes and Ears

The rest of the insects are, in general, much like the ants. They have their feelers or antennae, growing out in front of the head, with which they both feel and smell. Most of them seem to taste their food in their mouths. Nearly all have eyes.

As for ears, a good many insects, apparently, hear as the ants do, without any regular ears, and just by feeling the shake of what they happen to stand on. At least, nothing is known about their having any regular ears; though it is quite possible that some of them hear through their wings. Certainly, a tight hard wing, like a house fly’s, when one wasn’t using it for flying, ought to make a very decent sort of ear, one would think.

Grasshoppers and the like have proper ears. Though instead of being where we have ours, on the sides of our heads, Grasshopper Gray carries his ears on his hind legs, on the side of his great jumping thighs; while the ear itself, instead of looking like a human ear, is like a tiny drum—a tight thin head with a hollow underneath. Some other insects have their ears on the side of their bodies, about the middle. You can see these things for yourselves; they are not hard to find.

Some of the jelly-fishes have ears, not at all good ones, but still ears. Some also have eyes, not so good even as the ears, and not good for much anyway. But the same kind of jelly-fish doesn’t have both ears and eyes; whichever he gets, he goes without the other, having apparently not sense enough to manage both. As for the sea-cucumbers, they sometimes have more than fifty ears apiece, none of them good for much.

Most all of these simpler sorts of ear are much like tiny rattles. There is a hollow ball lined with nerves. Inside the ball is a small hard ear-stone, or a number of smaller grains of ear-sand. When a sound comes along, (for a sound is nothing but jar), it shakes the rattle, so that the little stone inside bangs against the nerves. Then the animal hears. In the cod fish these ear-stones are unusually large, as large as the end of one’s thumb; children sometimes call them lucky-bones, and use them for playings. We also have these little rattles, two in each ear, with ear-sand. But these, which are all there is to the ears of lowly creatures, are only a small part of our hearing machinery.

You will find the ears of lobsters and crayfish, which are little fresh water lobsters, just at the point where the smaller feelers, which are double at the end, join the body. These, too, are merely ordinary ear-rattles; you can make out the opening on the upper side of the feeler. Of course, you know the ears of the frog—the big spots on the side of the head, back of the eyes. These spots are the drums of the ears; the real ear, much like our own, is inside. We have such a drum, only it is at the inner end of the hole into the ear, where it is much safer than it would be outside.

The fish’s ear you cannot find. That is inside; and the fish hears through the bones of his head, just as we do when we hold a stick in our teeth and tap the end, while we keep our ears stopped with our fingers. But the long dark stripe which you see on many sorts of fish, running from the place where the neck would be if fishes had one, the whole length of the body to the tail, and also forward across the head and around the eye, only you can’t make it out so well there, this also is a sort of ear. In fact, the ear itself is really a part of this “lateral line” very much improved—so much improved that we human beings and the four-footed beasts and the birds haven’t found it worth while to keep the lateral line at all. But the newts and salamanders still have it.

As for eyes, of these also there are all sorts. The star-fish has five, one at the end of each of its five arms, a tiny black dot. The jelly-fishes, some of the commoner sorts at least, have their eyes, such as they are, where the long tentacles join the center of the bell underneath. Some of the worms have several hundred eyes; some have a pair of eyes on each of the dozen or twenty joints of the body. The leeches, the common blood-suckers which get on our legs when we go swimming, have ten pairs of eyes, all on the front end.

Oysters, clams, and other “bivalves” have their eyes along the edge of the shell. Many of the snails have them on stalks, which they can pull back into the head or push out. The snail in Mother Goose, that

“...put out her horns Like a little Kylo cow”

and frightened the four-and-twenty tailors, was really only putting out her eyes to see these valiant heroes. Some of the shell-less snails, or slugs, besides the eyes on the ends of their horns, have a lot more, occasionally nearly a hundred, sprinkled over the back.

Such eyes, however, are really not good for much. They serve to tell light from darkness. They let the creature know when a shadow falls on him—which is usually the shadow of something on the point of eating him up, so he gets warning and bolts. We ourselves can do as much with our eyes shut tight; and that’s about all most eyes will do wide open. There are not many really good eyes, till you get the single pair of the animals with back bones.

Still there is one very fair sort of eye, though not nearly so good as ours, and that is the strange compound eye of the insects.