Insect Stories

by Vernon L. Kellogg

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 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.

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 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 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, 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 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.