THE INCHWORM
One day Uncle Paul was in his garden engaged in an operation on his
pear-trees that greatly puzzled Emile and Jules. He had a pot of black,
sticky stuff with a strong smell, and was smearing it with a brush all
around the base of the trees. Oh, how One-eyed John would have laughed
if he had peeped through the hedge and seen Uncle Paul daubing the foot
of his pear-trees with black! But he would have been greatly in the
wrong, as is proved by what the boys’ uncle said to them that same
evening.
“What do you call that stuff you were putting on the trees this
morning?” Jules inquired.
“It is called tar, and is a substance derived from coal. To make
illuminating gas coal is put into large cast-iron vessels and heated
red-hot, all outside air being excluded meanwhile. The heat decomposes
the coal, which cannot burn for want of air. The products of this
decomposition are illuminating gas, tar, and coke, this last being a
kind of coal of metallic appearance, very porous and light. The gas and
the tar are drawn off through a pipe, the coke remaining in the
cast-iron vessel. Tar is a very black, sticky substance with a strong
odor repugnant to insects.”
“Then you put a coating of it around the tree trunks to keep off
insects?”
“Certain moths whose caterpillars I fear came through my hedge. The
girdle of tar put on at the base of the trunk is to prevent their
climbing to the branches to lay their eggs. In that way I protect the
fruit-trees from the caterpillars that a little later would destroy the
foliage.”
“But moths can fly well enough, and your tar wouldn’t stop them. If
they can’t reach the branches by climbing the trunk they will fly up to
them.”
“For a moth that flies, agreed. If on the contrary it cannot fly, but
has to content itself with walking, is it not true that the coating of
tar encircling the foot of the tree trunk will prove an impassable
obstacle? In the first place, the smell of tar is offensive to the
moth, and then if it ventures on the sticky girdle it will infallibly
become entangled and die, stuck fast in the tar.”
“That is plain,” assented Louis. “But are there any moths that can’t
fly?”
“There are.”
“Are the lazy things afraid to use their wings?” asked Emile. “Perhaps
they think it’s too much trouble.”
“How could they use them? They haven’t any to use, poor things.”
“That accounts for it, then. Moths without wings!”
“Yes, my boy, moths without wings. You shall see some. This one is
called by learned men phalæna geometra, which means geometer-moth You
will soon see why it is so named.”
“But it has wings, magnificent ones, all dotted with brown spots on a
yellowish background.”
“Yes, and I will add that the forward ones have dark stripes. Now what
do you think of this other moth?”
“That ugly thing isn’t a moth.”
“You judge by appearances, my dear child, and not by reality. This
ungainly creature laboriously dragging along its big, naked, yellowish
abdomen, with large black spots, is the female of the other moth.”
“I should never have guessed it.”
“Neither you nor a great many others. Henceforth you will know that
there are numerous species of moths whose females are either wingless
or equipped with such mere stumps of wings that they are unable to fly,
whereas the males invariably have well-developed wings. Now, the male
is not the one to be feared; it is the female with her eggs. The office
of the tar girdle at the foot of the tree is to arrest the moth when it
tries to climb to the branches where the laying takes place. Repulsed
by the odor, it turns back; or if it persists in its endeavors to pass,
it sticks to the tar and so perishes.”
“If the female laid her eggs somewhere else,” suggested Jules, “instead
of on the branches—for instance, on the ground—wouldn’t the
caterpillars know enough to climb the trees by themselves?”
“The tar barrier would still be there to stop them. Besides,
caterpillars hatched on the ground would hardly think of climbing the
tree to the place where, in the usual order, the hatching would have
taken place. As long as the customary conditions remain unaltered,
insects show an astonishing instinct; beyond these conditions they do
not know how to act.
“The caterpillar of the geometer-moth is gray with a yellow stripe
running lengthwise on each side. It has a curious way of walking common
to it and other caterpillars of the same group.
“These caterpillars are long and cylindrical in shape, and they usually
have but two pairs of false legs, at some distance from the true front
legs. In walking they first rest themselves on the forward legs and
then bring up the others by curving the body into a loop or ring. The
next movement is to raise the forward legs and advance them in a stride
as long as the creature itself, after which the body again bends into a
loop by the bringing up of the hind legs as before. These peculiar
strides give the worm the appearance of a pair of dividers getting over
the ground by alternately opening and closing its two legs. You might
say the creature surveys or measures the road it travels, and that is
why its moth is known as the geometer-moth. The common name of inchworm
applied to the caterpillar is familiar to you as referring to the
caterpillar’s length.
“Further characteristics are to be noted. Clinging to the branch solely
by their hind creepers, these worms remain for hours in the strangest
postures, the body stiff and motionless. You will see some stretched
out straight, some turned up behind, some arched in a semicircular
position. Not one moves, not one shows weariness in these uncomfortable
attitudes which demand an incredible amount of strength. You have
witnessed the feats of those strong-armed acrobats who, in the
side-show at the fair, seize a vertical bar with both hands and without
further support sustain themselves in the air, the body horizontal.
Inchworms do the same thing, but with this difference: whereas the
acrobats are exhausted in a few moments, the caterpillars keep their
balance all day if necessary.”
“Why do they do all those stunts?” was Emile’s question.
“They are not doing stunts, as you call it; they are simply using their
natural means of escaping observation on the part of their enemies. By
reason of their complete immobility, rigid posture, and grayish hue
they are confounded with the small dry twigs which they closely
resemble. Unless examined at very short range they deceive all eyes,
even those of birds, whose sight is so keen.”
“Ah, the crafty rogues! To stiffen themselves and stay perfectly still
so as to look like little dry twigs and in that way fool the birds that
would come and snap them up, is a very clever trick.”
“The name of leaf-stripper, which is also given to this moth, indicates
its way of living before it is transformed into the perfect insect. The
caterpillar gnaws the leaves of all fruit-trees without distinction,
and even of other trees, such as oaks, birches, and lindens. For trees
that have not been smeared with a tar girdle to stop the moths at
laying time there is but one mode of defense left, and that is not
nearly so good as the first: it is to shake the infested trees so as to
make the caterpillars fall, and then crush them.”
“I prefer the tar girdle,” said Louis.
“Yes, but it must be applied in time, in the autumn when the moths are
about to make their appearance.
“Another moth of this group, sometimes called the winter moth, has fore
wings of a grayish wine-color dotted with brown and striped crosswise
in a darker shade. The female is a little better favored than that of
the one we have just been considering, having wings of a sort, but too
rudimentary to admit of flying. It may be seen running over the ground
toward the end of autumn, when cold weather is approaching. Its tardy
appearance has earned it the name of winter moth. Like the moth of the
inchworm it climbs trees to lay its eggs, but can be prevented by the
use of tar on the trunk. Its eggs hatch in the spring, and the
caterpillars are full-grown by May. They are generally blackish, with
white, yellow, or green stripes running lengthwise. On leaving the egg
these caterpillars bore the buds of pear, apple, apricot, and other
fruit trees. Later they install themselves, one by one, between two
leaves, the edges of which they unite with threads of silk.”