SPIDERS AND SCORPIONS
Most people think that spiders are insects. But this is a very great
mistake, for they are just about as unlike insects as they can possibly
be.
Insects, for example, always have distinct heads. But spiders never do,
for their heads are so sunk and lost in their chests that you cannot
possibly tell where the one leaves off and the other begins. So that
spiders have their bodies divided into two parts only instead of into
three, as is always the case in the insects.
Then insects always have six legs; spiders always have eight. Insects
have wings; spiders have none. Insects have feelers; spiders have none.
Insects nearly always have a great many eyes, which are six-sided;
spiders never have more than eight eyes, which are round. And while
insects may have biting jaws, or sucking jaws, or a trunk, or a beak,
spiders always have poison-fangs, which no insect ever possesses.
So you see that as far as the outside of their bodies is concerned,
spiders are very different indeed from insects. And the differences
inside the body are just as great. Insects have no hearts, the only
blood-vessel in their bodies being one long tube which runs along the
back; but spiders have quite a big heart, and a good many arteries as
well. Insects have no lungs, but breathe by means of slender tubes which
run to every part of the body; but spiders have quite big lungs, in
which the blood is purified just as it is in our own. Insects have no
brains, but only bunches of nerves in different parts of their bodies;
but spiders have quite big brains. And besides this, while all insects
which spin silk produce it through their mouths, spiders always do so by
means of organs at the very end of the body. So that inside, as well as
outside, there is hardly any respect in which spiders and insects really
resemble one another.
The silk-organs of a spider are very wonderful indeed. Remember, in the
first place, that the silk, as long as it remains in the body of the
spider, is a liquid--a kind of thick gum, which is produced and stored
up in six long narrow bags, or glands. Then if you look at the end of a
spider's body through a good strong magnifying-glass--or, better still,
through a microscope--you will see several little projections, which we
call spinnerets. Now each of these spinnerets is covered with hundreds
of tinier projections still, every one of which has an extremely small
hole in the middle. And all these holes communicate, by means of very
slender tubes, with one of the silk-glands.
So what a spider does when it wants to spin its line is to squeeze a
little drop of silk into one of the spinnerets. It then just touches the
object to which the line is to be fastened, and draws its body away. And
as it does so a delicate thread comes out from every one of the
projections on the spinneret; and all these threads unite together into
one stout cord. That is why a spider's thread is so strong. It really
consists of several hundred separate threads all firmly fastened
together. And if the spider wants to spin a stronger line still, it can
unite all the threads coming from several spinnerets into one, so as to
make a very stout cord indeed.
Spiders use this silk for all sorts of different purposes. In the first
place, they use it for snaring insects.
THE GARDEN-SPIDER
Let us take for an example, the web of the common garden-spider. It is
to be seen in every garden, resting in the middle of its web; and you
may always recognize it by the white cross upon its back. But I don't
suppose that you have ever seen it spinning its net. For it always does
so very early in the morning, generally beginning before sunrise, so
that it may be quite ready for use as soon as the insects begin to fly.
First of all, the spider makes a kind of outer framework of very strong
silken cords, and fastens it firmly in position by stout guy-ropes of
the same material. Next, she carries a thread right across the
middle and fixes it down on either side. Then, starting from the center,
she carries thread after thread to the margin, carefully testing the
strength of each by giving it two or three smart pulls, and fastening it
firmly down. When she has finished this part of her task, the web looks
like a badly shaped wheel.
The next thing that the spider does is to spin a little silken platform
in the middle of her web to sit upon. And as soon as she has done this
she begins to spin the spiral thread. Beginning from the center, she
goes round and round and round, fastening the thread down every time
that it crosses one of the straight cords--the spokes, as it were, of
the wheel--until at last the web is finished. Then she goes to the
little platform in the middle, and there remains, upside down, waiting
for an insect to blunder into her net.
By and by, perhaps, a bluebottle fly does so. Then she shakes the web
violently for a few moments, so as to entangle it more thoroughly,
rushes down upon it, seizes it, and plunges her fangs into its body. But
if she catches a wasp or a bee she nearly always cuts it carefully out,
drops it to the ground, and then patches up the hole in her web. For she
knows perfectly well that wasps and bees can sting!
Would you like to know why it is that flies stick to the web as soon as
they touch it? The microscope shows us. All the way along, the spiral
thread is set with very tiny drops of liquid gum. So tiny are these
drops indeed, that there are between eighty and ninety thousand of them
in a large web! And would you like to know why it is that the spider
does not stick to the web as the flies do? Well, the fact is that only
the spiral thread is set with these little gummy drops, and that as the
spider runs about over her web she is most careful to place her feet
only on the straight threads, and never on the spiral line. Other
spiders, however, snare their prey in quite a different way.
THE MARMIGNATTO
This small spider, found on our western plains, is remarkable for
feeding on large insects, such as grasshoppers and field-crickets, which
it catches in an ingenious manner. It stretches a few silken threads
across a narrow path way, quite close to the ground, along which these
insects are likely to pass, and lies in wait just opposite until a
grasshopper or a cricket approaches. When it comes to the threads the
insect is sure to get at least one of its feet entangled. Then it stops,
and tries to shake itself free. The only result of its struggles, of
course, is that its other feet become entangled too; and while it is
struggling the marmignatto springs upon its back, fastens a silken
thread to it, springs down again, and fastens the other end to a
grass-stem close by. Over and over again it does this, and before very
long the unfortunate insect is firmly fastened down by hundreds of
threads, and is quite unable to break free, or even to move one of its
legs. Then the spider leaps upon its back once more, plunges its fangs
into its body, and proceeds to suck its blood.
HUNTING-SPIDERS
Perhaps you may have seen little hairy black spiders, with white
markings upon the upper part of their bodies, running about in an odd
jerky way on sunny fences and walls. These are called hunting-spiders,
because they hunt their prey instead of snaring it. You may see them
gradually creeping up to a fly, so slowly that they hardly seem to move,
and then suddenly leaping upon it when they are about two inches away.
Then spider and fly, locked in one another's embrace, go falling toward
the ground together. But they never reach it, for wherever a
hunting-spider goes it always trails a rope of silk behind it, and
fastens it down at intervals. So when it springs from the fence it is
brought up at once by its own thread, and swings in the air till its
victim is dead. Then it just climbs up its thread, and so gets back to
the fence.
BIRD-SPIDERS
These great spiders of the tropics hunt for prey in much the same way.
Only instead of catching flies on walls they prowl about the
branches of trees in search of small birds, springing upon them when
they are roosting at night, and killing them almost immediately by a
smart bite from their venomous fangs. These spiders, of course, are very
large. Indeed, the body of a full-grown bird-spider is as big as a man's
fist, while its great hairy legs cover nearly a square foot of ground
when they are fully spread out.
TRAP-DOOR SPIDERS
These famous spiders are found more or less commonly in all warm
countries. They all live in tunnels in the ground, which they dig by
means of their fangs; and as they do not want the situation of their
nest to be discovered, they carry the earth away to a little distance as
fast as they dig it up, and carefully hide it. Very often the hole which
they dig in this way is eighteen inches or two feet deep. And at the
bottom it always turns sideways for an inch or two, so that the general
shape of the burrow is very much like that of a stocking.
This hole is always dug in the side of a bank, so that when there is a
heavy fall of rain the water may run away without flooding it.
When the burrow is finished, the spider lines it throughout with two
sheets of silk. The outer sheet, which comes next to the earth, is
rather coarse in texture, and is quite waterproof, in order to keep the
tunnel dry. The inner one is very much finer and softer, so that the
little home may be as comfortable as possible.
As soon as the lining process is completed, the spider sets to work on
the trap-door. This she makes in the cleverest manner possible. First
she measures the doorway most carefully by the aid of her feelers. Then
she spins a thin silken pad of exactly the same size and shape. This is
sticky on the top, like the spiral thread of the web of the
garden-spider: and she sprinkles it all over with very small scraps of
earth. Upon this she fastens another silken pad, which she sprinkles
with earth in the same way. And then comes another and then another, and
so on till the door is sufficiently thick. Finally, she fastens it in
position by means of a hinge, which is also made of silk; and
she always places this hinge on the upper side of the doorway, so that
the door may fall down behind her by its own weight whenever she leaves
the burrow. She is rather a lazy creature, you see, and does not want to
have the trouble of shutting the door for herself! And if she left it
open, every passer-by would find out where she had made her home.
The door always fits most wonderfully into its place, and the spider
carefully covers the top with little bits of moss and small scraps of
earth and stone, so as to make it exactly like the surface of the ground
all round it. Indeed, unless one happens to see the spider push it open,
it is almost impossible to find it.
When one of these spiders is in her burrow, she always fastens about
half a dozen silken threads to the inner side of the door, carries them
down to the bottom, and sits with one of her feet resting upon each. No
one can then try to force her door open without her knowledge, and as
soon as she feels the least pull upon the threads she rushes up the
burrow, clings to the walls with her hind feet, seizes the door with her
front ones, and pulls it downward with all her might. And if the door is
forced open in spite of her efforts, she slips into a sort of side
tunnel which she always makes near the top of her burrow, and stays
there until the danger is past.
THE RAFT-SPIDER
There are several spiders which live on or in the water. One of these is
the raft-spider, which is found in the fen districts of England. If you
should happen to meet with it you can recognize it at once, for all
round the upper part of its body is a narrow band of yellow, and inside
this is a row of small white spots.
This spider is about an inch long, and owes its name to the fact that it
actually makes a little raft on which to go out searching for
water-insects. Collecting together a quantity of little bits of leaf and
cut grass and reeds, it fastens them firmly together with silken
threads, just as shipwrecked sailors might lash planks together with
ropes in order to escape from a sinking vessel. In this way it makes a
small floating platform, perhaps a couple of inches in diameter.
When the raft is finished, the spider gets upon it, pushes off from the
shore, and allows the current to carry it along. By and by, perhaps, it
catches sight of some water-insect floating at the surface, or of a
drowning fly which has fallen into the stream. Then it leaves its raft,
runs along over the surface of the water, seizes its victim, and carries
it back to the raft to be devoured. And if it should be alarmed, or
think itself in danger, it gets under the raft and clings to the lower
surface, so that it cannot be seen from above.
THE WATER-SPIDER
More curious still is the water-spider, which actually makes its nest
under water. This spider, which is almost black in color, and has a very
hairy body and legs, is common in ponds and canals, and spends almost
the whole of its life beneath the water. Its little silken nest is
shaped like a thimble, with the mouth downward, and is placed among
weeds, to which it is firmly fastened down by guy-ropes, also of silk.
And when it is finished the spider fills it with air. She does this in a
most curious manner. Rising to the surface, she turns upside down, pokes
her long hind legs out of the water, and crosses the tips. Then she
dives again, carrying down a big bubble of air between these hairy legs
and her equally hairy body as she does so. She next gets exactly
underneath the entrance to her nest and separates her legs. The result
is, of course, that the air-bubble floats up and occupies the upper
part. Another bubble is now brought down in the same way, and so the
spider goes on, fetching bubble after bubble, until at last her little
nest is completely filled with air. Then she gets inside it, and watches
for the grubs of water-insects to swim by.
In this wonderful nest the spider lays her eggs and brings up her
family. When the little ones have been hatched, of course, the air in
the nest very soon becomes too impure to breathe. Then the little
spiders cling tightly to the walls, while the mother gets outside and
tilts the whole nest sideways, so that all the exhausted air floats up
in one big bubble to the surface. Then she pulls the nest back into
position, hurries up to the top of the water and brings down a
bubble of air, and then another, and so on until the nest is filled with
air all over again.
If you ever catch one of these spiders, and keep it for awhile in a jar
of water with a little piece of water-weed, you may see it spinning its
wonderful nest, and filling it with air, perhaps half a dozen times a
day.
GOSSAMERS
Before we leave the spiders altogether, we must tell you something about
the wonderful little creatures called gossamers. These are really the
young of a good many different kinds of spiders. It often happens, of
course, that several families, with perhaps five or six hundred little
ones in each, are all living quite close to one another. The result is
that there is not sufficient food for them all. So they make up their
minds to go out into the world and seek their fortunes; and this is how
they do it.
Choosing a warm, sunny morning in the early part of the autumn, all the
little spiders climb the nearest bush, and each one makes its way to the
very tip of a leaf. Then, clinging firmly to its hold, it begins to pour
out a very slender thread of silk from one of its spinnerets. You know
that on warm, sunny days the air near the ground soon becomes heated and
rises, as hot air always does; and in rising it carries up these
delicate gossamer-threads, as they are called, with it. Still the little
spiders hold on, and pour out their lines, till at last each has several
feet of thread rising straight up into the air above it. Then suddenly
they all let go, and are carried up into the air at the ends of their
own threads. So they go on, up and up and up, till at last they meet a
gentle breeze, which carries them along with it. So, perhaps, they
travel for thirty, forty, or fifty miles, or even farther still. And
when at last they make up their minds to descend, all that they have to
do is to roll up the threads which have been supporting them, and down
they come floating gently back to earth. One good name for them is
ballooning spiders.
Haven't you sometimes found on a warm autumn morning that all the trees
and bushes, and even the grass and low plants, are quite covered
with threads of silk? The next time you see such a sight look carefully,
and you will find that on every thread a little baby spider is sitting.
Then you may be quite sure that all these little spiders set out early
in the morning to seek their fortunes, and that, borne up by their
slender threads, they have traveled for many long miles through the air.
SCORPIONS
These formidable creatures are closely related to the spiders. They are
found in all warm countries, with the exception of New Zealand, and may
easily be known by two facts. In the first place, in front of the legs
they have a pair of great, strong claws, which look very much like those
of a crab. And in the second place, the last five joints of the body are
narrowed into a long, slender tail, at the end of which is a claw-like
sting. When they attack an enemy, or seize a victim, they grasp it with
the claws, turn the tail over the back, and force the sting into its
body. And the poison which is introduced into the wound is so powerful
that the sting of a large scorpion is almost as severe as the bite of an
adder.
During the daytime scorpions hide away under stones and logs, or in
crevices in the ground, or perhaps under the loose bark of dead trees.
But very soon after sunset they come out from their retreats and prowl
about all night long in search of insects; and it is at such times that
they invade camps and houses, get into shoes, etc., and persons get
stung unless they are very careful.
CENTIPEDES AND MILLEPEDES
One can easily recognize centipedes by the great number of their feet.
The name centipede, indeed, means hundred-footed. None of these
creatures, however, have exactly a hundred limbs. Some only have fifteen
pairs of legs; some have as many as one hundred and twenty-one pairs.
But whether they be many or few, the number of pairs is always odd.
Another very curious fact about centipedes is that they have no
less than four pairs of jaws. But the fourth pair take the form of
fangs, which are very stout and strong, and very much curved, while at
their base, just inside the head, is a little bag of poison. In the
northern centipedes, which are quite small, the fangs are not large
enough, nor the poison sufficiently strong, to cause a serious wound.
But some of the tropical species, which grow to the length of nearly a
foot, are quite as venomous as the largest scorpions.
The food of these creatures consists chiefly of worms and insects. But
the larger ones will kill lizards, and even mice, and have been known to
prey upon victims actually larger than themselves.
The eggs of centipedes are laid in little clusters on the ground in some
dark, damp nook, and when they have all been deposited the mother
centipede coils herself round them, and there remains guarding them
until they hatch.
Millepedes, in some ways, are very much like centipedes; but they only
have two pairs of jaws instead of four, and they are nearly all
vegetable-feeders. The long, smooth, and slender _Julus_ millepedes
are plentiful in every garden. And in tropical countries they sometimes
grow to a length of six inches. Even the largest, however, are perfectly
harmless, for they have no poison-fangs as the centipedes have, and the
only way in which they ever attempt to defend themselves is by pouring
out a small drop or two of a fluid which smells rather nasty, and no
doubt protects them from the attacks of birds.