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 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, 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.
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, 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 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 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 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!
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.
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