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Insect Stories

<h2>HOUSES OF OAK</h2> There are eight different kinds of oak-trees growing on or near the campus where Mary and I live. And each kind of oak-tree has several kinds of houses peculiar and special to it. Which makes altogether a great many styles and sizes of houses of oak for Mary and me to get acquainted with. For we have made up our minds to know them all, and something about the creatures that live in them. This is a large undertaking, we are finding, but an intensely interesting and delightful one. Some of it is quite scientific, too, which makes us proud and serious. We are keeping notes, as we did about Argiope and the way it handled flies and bees, and some day we shall print[Pg 286] these notes in the proceedings of a learned society, and make a real sensation in the scientific world. Anyway we think we shall. Just now, however, we shall only tell the very simplest things about these houses of oak and their inhabitants, for we suppose you wouldn't be interested in the harder things; perhaps, indeed, not even understand them all. Although, as I have already said, there are eight different kinds of oak-trees growing in our valley and mountains, two of these kinds, the live-oaks and the white oaks, are by far the most common and numerous. As one stands upon the mountain tops or foothills and looks down and over the broad valley, all still and drowsy under the warm afternoon sun, it seems as if you were looking at a single great orchard with the trees in it in close-set regular lines and plots in some places, and irregularly scattered and farther apart in other places. Where they are regular and close together, [Pg 287]they really are orchard trees; where they are irregular and widely spaced and larger, they are the beautiful live-oaks and white oaks that grow in all the grain-fields and meadows and pastures of our valley. The live-oaks have small leaves, dark green and close together, and the head of the tree is dense and like a great ball; the white oaks have larger, less thickly set leaves of lighter green, and the branches are more irregular and straying and they often send down delicate pendent lines that swing and dance in the wind like long tassels. The live-oaks have leaves on all the year through; the white oaks lose theirs in November. <div class="figcenter"> <ANTIMG src="images/i036.jpg" width-obs="400" height-obs="508" alt="" /></div> In both of these kinds of trees the oak houses can be found, but especially in the white oaks. And there are, as I have said, many kinds of the houses. Mary and I have found little round ones, big bean-shaped ones, little star-shaped ones, slender cornucopia-like ones, green, whitish,[Pg 288] red-striped, pink-spotted, smooth, hairy, rough-coated, spiny ones, and still other kinds. Some of the houses are on the leaves, some on the leaf-stems, some on the little twigs, and some on the branches. Some of the houses stay in the trees all through the year, but most of them drop off in the autumn, especially in the white-oak trees, just as the leaves do. We go out and hunt for the houses in the trees and among the fallen leaves on the ground under the trees. They are sometimes, especially the little ones, hard to find, for their colors and shapes often seem to fit in with their surroundings, so as to make them very hard to see. But others, like the big ball-shaped white ones shown in Sekko Shimada's picture, are, on the contrary, very conspicuous. If the houses are on the ground, or even if they are still on the tree and we think they are all through being made—and there are various ways of knowing about this, but[Pg 289] the most important is the time of year—Mary and I bring them home with us and put them in little bags of fine cloth netting, tarlatan usually, the houses that are alike and from one place being put together in a single bag. Then we tie a string around the mouth of the bag and wait for the dwellers in the houses to come out. For one has to be careful about trying to see the oak-house dwellers before they are ready to come out. It is much better to await their own sweet pleasure in this matter, than to go digging or prying in, for the houses have no doors or windows until just at the time the dwellers come out! In fact they make the doors as they come out. You will see, after we tell you a little more, that this arrangement is a very good one. Even as it is, various unwelcome intruders find their way into the house much to the annoyance and even to the fatal disaster of the inmates. So we wait until the dwellers are ready[Pg 290] to come out. Or if occasionally we really think we ought to see how things are going on inside, we chop a house or two open and see what we can see. What this is, usually, is a house's insides very unusual and curious, for the rooms occupy so little space and the walls so much. Sometimes there is only one room and that right in the middle, all the rest of the house being just a dense or sometimes loose and spongy wall all around it. In the single room, or in each of the several rooms, we find a curled-up little shining white grub without legs, and of course without wings, and with a head that doesn't seem much like a head, for it has no eyes nor feelers, and most of the time is drawn back into the body of the grub so that it is hardly visible at all. But there is a mouth on this silly sort of head, and the grub eats. What it eats is part of its own house! The houses, or galls, as the entomologists call them, are of course not actually made[Pg 291] by the insects that live in them; they are made by the oak-tree on which they are. But they are only made at the demand, so to speak, of the insects. That is, the oak-galls are formed only where a gall-insect has pricked a live leaf or stem or twig with her sharp, sting-like little egg-layer, and has left an egg in the plant-tissue. Nor does the gall begin to form even yet. It begins only after the young gall-insect is hatched from the egg, or at least begins to develop inside the egg. Then the gall grows rapidly. The tree sends an extra supply of sap to this spot, and the plant-cells multiply, and the house begins to form around the little white grub. Now this house or gall not only encloses and protects the insect, but it provides it with food in the form of plant-sap and a special mass or layer of soft nutritious plant-tissue lying right around the grub. So the gall-insect not only lives in the house, but eats it! [Pg 292] After it is full-grown, the grub stops eating. Then the house, or gall, stops growing and becomes harder and changes from greenish to some other color, and, in most cases, pretty soon drops off the tree to the ground. The gall-insect is still alive inside, of course, but is perfectly quiet and is simply waiting. It is at this time in the life of the houses and their dwellers that Mary and I collect them and bring them home and put them into little tarlatan bags. This is autumn, the time that the trees in the East turn yellow and red, but in California do not. They just stay green, but get quiet or turn brown or simply drop off their leaves and stand bare. All through the autumn and winter the gall-insects do nothing inside their houses. Indeed we can take them out and keep them in little vials, and most of them get on very well. They require no food; they simply want to be let alone. But in early spring—and spring in California comes[Pg 293] very early; indeed, it comes in winter!—they wake up and in a short time change into stout-bodied little real insect-looking insects with six legs, four wings, a round head with feelers and eyes and whatever else an insect's head ought to have. Especially sharp jaws. For each gall-dweller has now to get out of its house. And as there are no doors, it has to make them. Which it does with its sharp jaws, gnawing a tunnel from the center of the house right out through the thick hard wall to the outside. When it gets out it flies around in lively manner for a few days, finally settling on a sprouting oak-leaf or bud or green stem or twig, and laying a few eggs, or several, or many, according to the habits of its special kind, and then it dies. And when the tiny white grubs hatch from these eggs, new houses begin to be made around them by the oak-trees, and a new generation of gall-insects is fairly started. [Pg 294] But not all the dwellers in the houses of oak have such a smooth and easy life as I have described. There will often come out of one of the galls that Mary and I have in a tarlatan bag, not one kind of insect, but several kinds, and only one of these kinds is the regular proper house-owner. The others are interlopers. Some of them may be only uninvited but not especially harmful guests, just other kinds of gall-insects that seem to have given up the habit—if they ever had it—of starting houses of their own, and have adopted the cuckoo-like way of laying their eggs in the just-starting houses of other gall-insects. The grubs, or young of these messmate gall-insects, live in, and feed on, the same house, with the rightful dwellers, but as the oak-tree has plenty of sap and the gall-house is usually large enough for all, there is generally no harm done by these cuckoo intruders. But some of the intruding insects that[Pg 295] come from our galls are not so harmless. They are the ones called parasites. They live in the houses not for the sake of the protection or the food furnished by the house, but in order to eat the actual dwellers in the house. Often and often not a single real gall-insect would come out in the spring from many of our collected houses, but only a little swarm, or sometimes just two or three or even one, of these insect-devouring parasites that has eaten up the rightful owners of the houses. There are other enemies, too, of the oak-house dwellers. Birds like to peck into the soft, growing galls to get at the tidbits inside. And predaceous beetles and other strong-jawed insects with a fondness for helpless, soft-bodied, juicy grubs would like to gnaw into the houses. So the houses have to protect the dwellers inside, and they do this in various ways. Some are extra thick-walled or have an extra-hard[Pg 296] outer shell. Some are covered with spines or hairs. Some have a viscous gluey excretion, some have a very bad odor, some are so colored and patterned that they are very hard to distinguish from the foliage or from the fallen leaves around them, and, finally, some secrete a sweetish honey-dew which attracts ants, and these fierce visitors, who are content with the honey-dew, probably drive away many visiting parasites and predaceous insects. But it would be tiresome to go on and tell you all the things we are finding out about the houses of oak and the insects that live in them. Of how we have got them to lay their eggs right before our eyes on little fresh branches that we bring into the house. Of how the houses begin to form under the bark or leaf surface as mere little swellings and then break through and get larger and larger and take on their characteristic form and color. Of how we have to study the gall-dwellers with a microscope,[Pg 297] for the largest that we have found yet—the ones that make the big galls shown in Sekko's picture—are only one-fifth of an inch long, while others are not more than one-twenty-fifth of an inch long. Of how some kinds have to lay their eggs always on the same kind of oak-tree, while others prick different kinds of oaks. Nor can we tell of the questions and problems that we are trying to answer. As why it is that two galls made by two different kinds of gall-insects, but in the same parts, as leaves, of the same oak-tree, should be so different, or why the galls in different kinds of trees, though made by the same kind of insect, should be alike, as they usually are. And why with some kinds of the house-dwellers the children grow up to be different from the mother, but their own children grow up like the grandmother, and different from themselves. Or how they know not to lay too many eggs in one place, the ones making[Pg 298] little galls often laying several to many eggs in one leaf, but the ones making large galls being careful to lay only one egg in a leaf. And a lot of other things that they do that need explaining. Perhaps we shall find out the reason for some of these things. But naturalists have known the houses of oak-insects for two hundred years now, and if they haven't found the answers to some of these questions yet, perhaps no one ever can. But that isn't a good way to look at Nature. And so Mary and I don't. We think we may make a great discovery any day. We are like prospectors in the gold mountains. We never give up; we always keep prying and peering. The worst of it is, I suppose you think, that we always keep talking too. Well, this is the last sentence of this dose of talking; or next to last. For this is the END <div style="break-after:column;"></div>

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