INSECTS (Continued)
We now come to a very large and important order of insects indeed--that
of the _Hymenoptera_. This name means membrane-winged, and has been
given to them because their wings are made of a transparent membrane
stretched upon a light horny framework. It is not a very good name,
however, for many insects which do not belong to this order at all have
their wings made in just the same way. All the _Hymenoptera_,
however, have the upper and lower wings fastened together during flight
by a row of tiny hooks, which are set on the front margin of the lower
pair, and fit into a fold on the lower margin of the upper ones.
BEES
The bees belong to this order, and most wonderful insects they are--so
wonderful, indeed, that a big book might easily be written about them.
They are divided into two groups, namely, social bees and solitary bees.
The social bees are those which live together in nests; and our first
example, of course, must be the hive-bee.
In every beehive there are three kinds of bees. First, there are the
drones, which you can easily tell by their stoutly built bodies and
their very large eyes. They are the idlers of the hive, doing no work at
all, and sleeping for about twenty hours out of every twenty-four. For
six or eight weeks they live only to enjoy themselves. But at last the
other bees become tired of providing food for them. So they drive them
all down to the bottom of the hive and sting them to death one after
another. And that is the end of the drones.
Next comes the queen, the mistress of the hive. You can easily recognize
her, too, for her body is much longer and more slender than that
of the other bees, and her folded wings are always crossed at the tips.
The other bees treat her with the greatest respect, never, for example,
turning their backs toward her. And wherever she goes a number of them
bear her company, forming a circle round her, in readiness to feed her,
or lick her with their tongues, or do anything else for her that she may
happen to want. Her chief business is to lay eggs; and she often lays
two or three hundred in the course of a single day.
Lastly, there are the workers. There are many thousands of these, and
they have to do all the work of the hive, making wax and honey, building
the combs, and feeding and tending the young.
The comb is made of six-sided cells, and is double, two sets of cells
being placed back to back. Some of these cells are used for storing up
honey. But a great many of them are nurseries, so to speak, in which the
grubs are brought up. These grubs are quite helpless, and the nurse-bees
have to come and put food into their mouths several times a day.
Fastened to the outside of the combs, there are always several cells of
quite a different shape. They are almost like pears in form, with the
smaller ends downward. These are the royal nurseries in which the queen
grubs are brought up.
Bees feed their little ones with a curious kind of jelly, made partly of
honey and partly of the pollen of flowers. This is called bee-bread; and
it is rather strange to find that one kind of bee-bread is given to the
grubs of the drones and the workers, while quite a different kind is
given to those of the queens.
You will want, of course, to know something about the sting of the
bee--though perhaps you already know enough of the pain it can give!
This is a soft organ, enclosed in a horny sheath, with a number of
little barbs at the tip. When a bee stings us, it is often unable to
draw the sting out again, because of these barbs. So it is left behind
in the wound, and its loss injures the body of the insect so severely
that the bee very soon dies. The poison is stored up in a little bag at
the base of the sting, which is arranged in such a way that when the
sting is used a tiny drop of poison is forced through it, and so enters
the wound.
Then, no doubt, you would like to know how bees make honey; but
that neither we nor any one can tell you. All we know is, that the bee
sweeps out the sweet juices of flowers with its odd brush-like tongue
and swallows them; that they pass into a little bag just inside the hind
part of its body, which we call the honey-bag; and that by the time the
bee reaches the hive they have been turned into honey. But how or why
the change takes place no one knows at all.
Bumblebees, or humblebees, are also social bees; but their nests are not
quite as wonderful as those of the hive-bee, and their combs are not so
cleverly made.
One of these bees is called the carder, and you may sometimes find its
nest in a hollow in a bank. But it is not at all easy to see, for the
bee covers over the hollow with a kind of roof, which is made of moss
and lined with wax. And this looks so like the surrounding earth that
even the sharpest eye may often pass it by. When this roof is finished,
the bee makes a kind of tunnel, eight or ten inches long and about half
an inch in diameter, to serve as an entrance; and this is built of moss
and lined with wax in just the same way.
On a warm sunny day in spring you may often see one of these bees flying
up and down a grassy bank searching for a suitable burrow in which to
build. Then you may be quite sure that she is a queen. For among
bumblebees the drones and workers die early in the autumn, and only the
queens live through the winter.
Solitary bees are very common almost everywhere, and you may find their
nests in all sorts of odd places. One kind of solitary bee, for example,
builds in empty snail-shells, and another in small hollows like
keyholes. A third gnaws out a burrow in the decaying trunk of an old
tree, or in the timbers of a barn or house-porch and makes a number of
thimble-shaped cells out of little semicircular bits of rose-leaf, which
it cuts out with its scissor-like jaws. Haven't you noticed how often
the leaves of rose-bushes are chipped round the edges, quite large
pieces being frequently cut away? Well, that is the work of the
leaf-cutter bee, as this insect is called, and very often not a single
leaf on a bush is left untouched.
But the commonest of all the solitary bees burrows into the
ground. As you walk along the pathway through a meadow in spring, you
may often see a round hole in the ground, just about large enough to
admit an ordinary drawing-pencil. That is the entrance to the burrow of
a solitary bee; and if you could follow the tunnel down into the ground
you would find that it was about eight or ten inches deep, and that at
the bottom were four round cells. In each of these cells the bee lays an
egg. Then it fills the cells with flies, or spiders, and caterpillars,
or beetles, for the little grubs to feed upon when they hatch out. For
solitary bees do not nurse their little ones, as social bees do, and
feed them several times a day. But at the same time the grubs are quite
helpless, and cannot possibly go to look for food for themselves. So the
mother bee has to store up sufficient to last them until the time comes
for them to spin their cocoons and pass into the chrysalis state. These
are only a few examples of a large number of interesting ways in which
the solitary bees in various parts of the world provide for their young.
WASPS
Wasps make nests which are almost as wonderful as those of the hive-bee.
That of the common yellow-jacket wasp is generally placed in a hole in
the ground, or in a cavity under a stone, and is made of a substance
very much like coarse paper, which the wasps manufacture by chewing wood
into a kind of pulp. You may often see them sitting on a fence, or on
the trunk of a dead tree, busily engaged in scraping off shreds of wood
for this purpose. When the nest is finished it is often as big as a
football, and of very much the same shape; and inside it are several
stories, as it were, of cells placed one above another, and supported by
little pillars of the same paper-like material. These cells are
six-sided, like those of the hive-bee, but they are squared off at the
ends, instead of being produced into pointed caps, and they always have
their mouths downward. In a large nest there may be several thousands of
these cells, and very often three generations of grubs are brought up in
them, one after the other.
The hornet, which is really a kind of big wasp, makes its nest in just
the same way, but places it on a beam in an out-house, or in a hole
which the sparrows have made in the thatched roof of a house, or in a
hollow tree, or perhaps hangs it in the open air to the bough of a tree.
ANTS
Even more wonderful than bees and wasps are the ants, which sometimes do
such extraordinary things that we are almost afraid to tell you about
them, for fear that you might not believe us. There are ants, for
example, which actually take other ants prisoners and make them act as
slaves, forcing them to do all the work of the nest, which they are too
lazy to do themselves; and there are ants which keep large armies,
sometimes more than one hundred thousand strong; and there are many ants
which harvest grain and store it away in underground barns! Many ants,
too, keep little beetles in their nests as pets, and fondle and caress
them just as one might pat a dog, or stroke a favorite cat. They even
allow them to ride on their backs; while, if the nest is opened, the
first thing they think of is the safety of their pets which they pick up
at once and hide away in some place of safety, even before they carry
off their own eggs and young. They also pet tiny crickets and small
white wood-lice in just the same way.
Then ants have little "cows" of their own, which they "milk" regularly
every day. These are the greenfly or aphis insects which do so much harm
in our gardens and fields, plunging their beaks into the tender shoots
and fresh green leaves of the plants, and sucking up their sap
unceasingly. And as fast as they do so they pour the sap out again
through two little tubes in their backs, in the form of a thin, sticky,
very sweet liquid which we call honeydew. Now the ants are very fond of
this liquid, and if you watch the greenfly insects which are almost
always so plentiful on rose-bushes, you may see the ants come and tap
them with their feelers. Then the little creatures will pour out a small
quantity of honeydew from the tubes on their backs, which the ants will
lick up. That is the way in which ants milk their little cows,
and they are so fond of the honeydew that they will carry large numbers
of these aphides into their nests and keep them, like a herd of cattle,
all through the winter, so that they may never be without a supply of
their favorite beverage!
Ants, like bees and wasps, almost always consist of drones, queens, and
workers. Only the drones and queens have wings, and these are seldom
seen until the end of August. But then they make their appearance in
vast swarms, which are sometimes so dense that from a little distance
the insects really look like a column of smoke. They only take one short
flight, however, and when this is over they come down to the ground and
snap off their wings close to their bodies, just as termites do.
One of the most curious of all these insects is the parasol-ant, of
South America, which makes enormous dome-shaped nests of clay. But as
the clay will not bind properly by itself, the insects work little
pieces of green leaf up with it. These pieces of leaf are generally
obtained from an orange plantation, perhaps half a mile distant. And
when the ants are returning from their expedition, each holds its little
piece of leaf over its head as it marches along, just as if it were
carrying a tiny green parasol!
Another very famous ant is the African driver, which owes its name to
the way its vast armies drive every living creature before them.
Insects, reptiles, antelopes, monkeys, even man himself, must give way
before the advancing hosts of the drivers; for it is certain death to
stand in their path.
SAW-FLIES
The saw-flies also belong to the order of the _Hymenoptera_. These
flies are so called because the female insects have two little saws at
the end of the body, which work in turns, one being pushed forward as
the other is drawn back. With these they cut little grooves in the bark
of twigs, or in the midribs of leaves, in which they place their eggs by
means of the ovipositor between the saws.
Some of these insects are extremely mischievous. The grub of the
turnip saw-fly, for instance, often destroys whole fields of turnips,
while the currant saw-fly is equally destructive to currants and
gooseberries. One often sees bushes which it has entirely stripped of
their leaves.
You may always know a saw-fly grub by the fact that it has no less than
twenty-two legs--three pairs of true legs on the front part of the body,
and eight pairs of false legs, or prolegs, as they are often called, on
the hinder part.
There is one little family of saw-flies, however, which are quite unlike
all the rest, for instead of having saws at the ends of their bodies,
they have long boring instruments, very much like brad-awls. With these
they bore deep holes in the trunks of fir-trees, in order to place their
eggs at the bottom; and the grubs feed, when they hatch out, on the
solid wood.
These insects are known as horn-tailed saw-flies, and one, which is very
common in pine woods, is very large, sometimes measuring an inch and a
half from the head to the tip of the tail, and very nearly three inches
across the wings, while the boring tool is fully an inch long. It is a
very handsome insect, and looks rather like a hornet, the head and
thorax being deep glossy black and the hind body bright yellow, with a
broad black belt round the middle. The feelers are also yellow, and the
legs are partly yellow and partly black.
GALL-FLIES
Another group of the _Hymenoptera_ consists of the gall-flies.
These are all small insects, which lay their eggs in little holes which
they bore in roots, twigs, and the ribs and nervures of leaves. In each
hole, together with the egg, they place a tiny drop of an irritating
liquid, which causes a swelling to take place, on the substance of which
the little grub feeds. Sometimes these galls, as they are called, take
most curious forms. The pretty red and white oak-apples of course you
know; and no doubt, too, you have often found the hard, woody,
marble-shaped galls which are so common on the twigs of the same tree.
Then some galls look like bunches of currants, and some look like
scales, and some look like pieces of sponge. And if you cut one
of them open you will find perhaps one little grub, or perhaps several,
curled up inside them.
[Illustration: LEAF-EATING INSECTS OF SHADE-TREES.
TUSSOCK MOTH: 1, caterpillar (black and yellow, head red); 2, male
moth (mottled gray); 3, wingless female laying eggs on her recently
vacated cocoon; 4, cocoons; 5, cast skins of young caterpillars; 6,
work of youth caterpillars under the surface of a leaf; 7, male
pupa; 8, branch girdled by caterpillar; 9, broken end of girdled
twig.
FOREST TENT-CATERPILLAR: 10, female moth (buff); 11, male moth
(rust-red); 12, egg-belt; 13, fully grown caterpillar, or
"maple-worm" (dull blue, red-streaked); 14, cocoon in leaf; 15,
pupa; 16, cast skins.]
ICHNEUMON-FLIES
This is the last group of _Hymenoptera_ that we can mention. These
insects lay their eggs in the bodies of caterpillars or chrysalids, and
sometimes in those of spiders, boring holes to receive them by means of
their little sting-like ovipositors. Before long the eggs hatch, and the
little grubs at once begin to feed upon the flesh of their victims. For
some little time, strange to say, the unfortunate creature seems to
suffer no pain, or even discomfort, but goes on feeding and growing just
as before, although hundreds of hungry little grubs may be nibbling away
inside it. Sooner or later, however, it dies; and then the little grubs
spin cocoons and turn to chrysalids, out of which other little flies
appear in due course, just like the parents.
Millions of caterpillars are destroyed by these little flies every year.
Out of every hundred of those which do so much damage to our cabbages
and cauliflowers, for example, at least ninety are sure to be "stung."
Indeed, if it were not for ichneumon-flies we should find it quite
impossible to grow any crops at all, for they would all be eaten up by
caterpillars.
LEPIDOPTERA
Next we come to the butterflies and moths, which are called
_Lepidoptera_, or scale-winged insects, because their wings are
covered with thousands upon thousands of tiny scales. If you catch a
butterfly, a kind of mealy dust comes off upon your fingers, and if you
look at a little of this dust through a microscope, you find that it
consists simply of little scales, of all sorts of shapes. Some are like
battledores, and some like masons' trowels, and they are nearly always
most beautifully sculptured and chiseled. These scales lie upon the wing
in rows, which overlap one another like the slates on the roof of a
house. And sometimes there are several millions on the wings of a single
insect.
BUTTERFLIES
It is possible here, of course, to mention only a few of the most
striking forms of butterflies, out of the many hundreds of species
counted as North American. It may be said that these insects are much
alike in general features all round the northern half of the globe, the
same families being represented, so that, at first glance, European or
Asiatic examples of such butterflies as the great yellow, black-striped
swallowtail seem the same as American examples.
Among the handsomest of all northern butterflies is the purple emperor,
which you may sometimes see flying round the tops of the tallest trees
in large woods in the south of England. Far commoner, however, are the
large, small, and green-veined whites, whose caterpillars are so
destructive to cabbages; the scarlet admiral, with broad streaks of
vermilion across its glossy black wings; the peacock, with its four
eye-like blue spots on a russet ground; the tortoise-shells, mottled
with yellow and brown and black; and the pretty little blues, which one
may see in almost every meadow from the middle of May till the end of
September. Then there are the brimstone, with its pale yellow wings,
which with the blues dance along the roadways in little whirling
companies all summer; the meadow-brown and the large heath, to be seen
in thousands in every hayfield; the small heath and the small copper,
even more plentiful still; the fritillaries, some of which live in
woods, and some on downs, and some in marshy meadows; the pretty
orange-tip, with pure white wings tipped with yellow; and the odd little
skippers, which flit merrily about grassy banks in the warm sunshine in
May and again in August--besides several others, which are so scarce or
so local that hardly anybody ever sees them.
MOTHS
You can easily tell moths from butterflies by looking at their antennæ,
or feelers, which have no knobs at the tips, as those of
butterflies have. Their number also is very great, and we can mention
only a few of the most remarkable.
First among these is the splendid death's-head sphinx, or hawk, the
largest of all the insects, which sometimes measures five inches from
tip to tip of its wings when they are fully spread. It owes its name to
the curious patch of light-brown hairs on its thorax, which looks just
like a skull. The caterpillar is a huge yellowish creature, often nearly
six inches long, with a blue horn at the end of its body, and seven blue
stripes, edged with white, on either side. It lives in potato-fields,
hiding underground by day and coming out at night to feed upon the
leaves. And it is an odd fact that both the caterpillar and the perfect
insect have the power of squeaking rather loudly. The moth appears in
October.
The humming-bird hawk-moth flies by day, and you may often see it
hovering over flowers in the garden, with its long trunk poked down into
a blossom in order to suck up the sweet juices. As it does so it makes
quite a loud humming noise with its wings, like the little bird from
which it takes its name. And sometimes you may see a bee-hawk, which has
transparent wings, hovering in front of rhododendron blossoms in just
the same way.
The swifts fly between sunset and dark, and the largest of them is very
curious indeed. For although it has glossy white wings, so that one can
see it quite clearly in the dusk, it will suddenly disappear. The fact
is that although its wings are white above they are yellowish brown
below; so that when it suddenly settles, and folds them over its back,
it at once becomes invisible.
The goat-moths are large, heavily built insects, with brownish-gray
wings marked with a number of very short upright dark streaks. The
caterpillar is a great reddish-brown creature with a broad chocolate
band running down its back. It lives for three years in the trunks of
various trees, and then spins a silken cocoon in which to turn to a
chrysalis.
Tiger-moths have brown fore wings streaked with white, scarlet hind
wings with bluish-black spots, and bright scarlet body. The caterpillar,
which is very common in gardens, is generally called the woolly
bear, because of the long brown hairs which cover its body.
Very beautiful indeed are the burnets, which have dark-green front
wings, with either five or six large red spots, and crimson hind wings,
edged with black. You may often see them resting on flowers and
grass-stems by the roadside in the hot sunshine. And in some parts of
the country the cinnabar-moth is almost equally plentiful. You can
recognize it at once by the crimson hind wings, and by the streak and
the two spots of the same color on the front ones. The caterpillar,
which is bright orange in color, with black rings round its body, feeds
upon ragwort.
THE CURIOUS VAPORER
The vaporer-moth is very common toward the end of summer, and even in
London one may often see it dashing about in the hot sunshine with a
strange jerky flight. But one only sees the male, which is a bright
brownish-yellow insect measuring about an inch across the wings; for the
female is much more like a grub than a perfect insect, and has wings so
small that they are hardly visible. Of course she cannot fly; and her
body is so big and clumsy that she cannot even walk. So she spends her
life clinging to the outside of the cocoon in which she passed the
chrysalis state, and covers it all over with her little round white
eggs. And when she has laid the last of these she falls to the ground
and dies.
Very handsome indeed is the emperor-moth, which has a big eye-like spot
in the middle of each wing, something like those of the
peacock-butterfly. But its caterpillar is even more beautiful still, for
its body is of the loveliest grass-green color, sprinkled all over with
little pink tubercles, each of which is enclosed in a ring of black, and
has a tuft of glossy black hairs sprouting from it. This caterpillar
feeds on bramble and heather, and when it reaches its full size it spins
a light-brown cocoon among the leaves of its food-plant, and then turns
to a chrysalis, from which the perfect moth hatches out in the following
April.
Very often one finds caterpillars which look just like little bits of
stick, and which walk in a most curious fashion by hunching up
their backs into loops, and then stretching them out again, just as if
they were measuring the ground. These caterpillars are called loopers,
and they turn into moths with large broad wings and very slender bodies.
There are a great many kinds of these moths. One, called the
swallowtail, may often be found hiding among ivy in July. It has large
wings of a pale-yellow color, with little tails upon the hinder pair.
Then there are the sulphur, a smaller insect with wings of a brighter
yellow; the emeralds, of the most delicate green; the magpie, which has
wings of the purest white, marked with streaks of orange and numbers of
almost square black spots and blotches; and many others far too numerous
to mention. If you ever shake a bush in summer-time you may see quite a
dozen of them flying away to seek for some fresh hiding-place.
Then there is a large moth known as the puss, because it is colored
rather like a brindled gray cat. The caterpillar is bright green, with a
big hump in the middle of its body, and two long thread-like organs at
the end of its tail, with which it will sometimes pretend to be able to
sting you. But in reality it is perfectly harmless. You may often find
it feeding on the leaves of willow-trees in August, and when it is fully
fed it spins a hard, oval cocoon in a crack in the bark. And there are
three smaller moths belonging to the same family, which are known as
kittens!
Another very large group of moths is that of the _Noctuæ_, or
night-fliers. But we so seldom see these unless we go out specially to
look for them that we shall pass them by without further mention.
HOMOPTERA
The next order is that of the _Homoptera_, or same-winged insects,
which are so called because their upper and lower wings are just alike.
The froghoppers all belong to this order. Do you know them? They are
little brown or gray insects, sometimes marked or marbled with white,
which carry their wings folded tentwise over their backs, and hop about
with really wonderful activity. It has been calculated that if a
man of ordinary height could leap as well as a froghopper, in proportion
to his greater size, he would be able to cover nearly a quarter of a
mile at a single jump!
But if you do not know the froghoppers by sight you must at any rate
know something of their grubs; for these are the creatures which cause
the cuckoo-spit of which one sees so much during the early summer. Very
often the weeds and long grass in a meadow, or by the roadside, are
almost covered with the odd little masses of froth, so that one's feet
get quite wet as one walks through the herbage. And in the middle of
each mass is a fat little grub, which is sucking up the sap of the plant
upon which it is resting, and pouring it out again in frothy bubbles.
The mischievous little aphides, or greenfly insects, also belong to this
order. There are many different kinds, some of which do terrible damage
to hops and corn and all sorts of cultivated plants. We have already
mentioned these when describing the habits of ants, and you will
recollect that they have sharp little beaks, which they thrust into
young shoots and tender leaves in order to suck up the sap; and that as
fast as they do so they pour it out again through two little tubes upon
their backs in the form of the thin, sweet, and very sticky liquid which
we call honeydew. You will remember, too, how fond ants are of this
liquid, and how they "milk" the tiny insects just as if they were little
cows.
So, you see, the aphides injure plants in two ways. First, they draw off
all their sap, which is really their life-blood; and then they drop this
sticky honeydew on to the leaves below, and choke up the little holes by
means of which they breathe. And the worst of it is that these insects
multiply so rapidly. Where there is one to-day there will be five and
twenty to-morrow; and two days later there will be five and twenty times
five and twenty; and two days later still there will be five and twenty
times five and twenty times five and twenty! Indeed, if it were not for
ladybirds and lacewing flies and one or two other insects which feed
upon aphides, every green leaf would be destroyed by them in a few
months' time.
A very curious fact about these insects is that as long as they
can find plenty of food they do not grow any wings. But as soon as the
sap becomes scanty or thin, wings make their appearance, so that they
can fly away and seek for better food elsewhere.
HETEROPTERA
The order of the _Homoptera_, or same-winged insects, is followed
by that of the _Heteroptera_, or different-winged insects, in which
that part of the wings nearest to the body is hard and leathery, while
the rest is softer and thinner, and is generally almost transparent.
Some of these live upon land, while others spend most of their lives in
the water.
The curious bishop's-miters belong to the former group. There are a good
many kinds, and some of them are very common. You may see them sitting
upon flowers, or resting upon raspberries and blackberries in the
sunshine. But although they are sometimes very pretty, we do not advise
you to handle them, for they have the power of pouring out a liquid
which will make your fingers smell very nasty indeed. And you should be
most careful not to eat any fruit on which they have been resting, for
they leave a horrible flavor behind them, which is even worse than the
smell.
Among those which live in the water there are several most interesting
insects. There are the water-striders, for example, which you can see
running about on the surface of any pond, and which look like
narrow-bodied long-legged spiders. But you will notice that they only
have six legs, whereas true spiders always have eight. They skim about
on the water by means of the middle and hinder limbs, the front pair
being used in catching prey. And when they have caught a victim they
suck its juices through their sharp little beaks.
Then there is the water-boatman, which always swims on its back. The
reason why it does so is that when its body is in that position it is
shaped just like a boat, while its long hind legs serve as a pair of
oars. So the little insect really rows itself through the water. On a
bright sunny day you may often see it resting on the surface of a pond,
with its hind legs thrown forward in readiness for a stroke. And
if even your shadow falls upon it, or it feels the vibration of a heavy
footstep, it will dive down in a moment to some hiding-place among the
weeds.
If you ever catch a water-boatman, be careful how you handle it, or it
will give your finger a very painful prick with its sharp beak.
The water-scorpion, too, is very curious. It is a flat, oval insect, of
a dirty-brown color, which looks very much like a piece of dead leaf. It
seems to know this quite well, for when it is hungry it always hides
among dead leaves down at the bottom of the water, and keeps perfectly
still. Then the other insects do not notice it, and as soon as one of
them comes within reach it seizes it with its great jaw-like front legs,
and plunges its beak into its body.
This insect is called the water-scorpion because it has a long spike at
the end of its body, which looks something like a scorpion's sting. It
is really a breathing-tube, however, the top of which is poked just
above the surface of the water while the insect is lying at the bottom,
so as to enable it to breathe quite easily.
APHANIPTERA
The order of the _Aphaniptera_, or unseen-winged insects, is a very
small one, consisting only of the fleas. The name has been given to them
because their wings are so tiny that, even with the microscope, they can
hardly be seen at all.
There are a good many different kinds of fleas, all of which suck the
blood of animals through their sharp little beaks. Some of them are able
to leap to a really wonderful distance, by means of their powerful hind
legs. And they are so wonderfully strong that if a man were equally
powerful, in proportion to his greater size, he would easily be able to
drag a wagon which a pair of cart-horses could scarcely move!
DIPTERA
The last order of insects is that of the _Diptera_, or two-winged
flies, which seem to have two wings only instead of four. But if you
look at them closely, you will see a pair of little knob-like
organs just where the hind wings ought to be. And these little organs,
which we call balancers, are really the hind wings in a very much
altered form.
Although they are so tiny, and look so useless, these balancers are used
in some way during flight; for if they are damaged or lost the insect
can no longer balance itself or direct its course in the air.
THE MOSQUITO
The mosquito is a troublesome insect which most of us know only too
well; for there are very few of us who have not suffered from the wounds
caused by its beak. Its life-history is very interesting. The eggs,
which are shaped just like tiny skittles, are laid in the water, and the
mother gnat fastens them cleverly together in such a way that they form
a little boat, which floats on the surface. After a time a little door
opens at the bottom of each egg, and a tiny grub tumbles out into the
water. It is a very odd-looking little creature, with a very small head,
a very big thorax, and a very long tail; and it mostly floats in the
water with its head downward, and the tip of its tail resting just above
the surface.
These grubs feed on the little scraps of decaying matter which are
always floating in the water of the pond, and they wriggle their way
about in the strangest manner, by first doubling up their bodies and
then stretching them out, over and over again. After a time they throw
off their skins and change to chrysalids, and out of this, a few days
later, the perfect gnats make their appearance.
The mosquito is a gnat that has many relatives, some very troublesome,
like the black fly. Some gnats have very big bushy feelers, just like
big plumes. These are the males, and you need not be afraid of them, for
they have no beaks and cannot bite.
CRANE-FLY AND DRONE-FLY
Then there is the crane-fly, whose balancers you can see quite easily.
This insect lays it eggs in the ground, and the grubs which
hatch out from them are called leather-jackets, because their skins are
so very tough. They feed upon the roots of grass, and sometimes do a
great deal of mischief in pastures. Indeed, if it were not for such
birds as the crow and meadow-lark, which destroy them in enormous
numbers, we should find it almost impossible to grow any grass at all.
The drone-fly really does look rather like a bee; but it only has two
wings instead of four, while its body is much more stoutly built, and it
has no sting, so that you need not be in the least afraid of it. You may
often see it sitting on flowers on sunny days in autumn, and it is
especially fond of those of the ragwort.
The grub of this fly spends its whole life buried head downward in the
mud at the bottom of some shallow pool--thick, black mud, which is
largely made up of decaying leaves--and never comes out of it even to
breathe. But at the end of its body it has a long tube, the tip of which
rests just above the surface of the water, so that it can draw down as
much air as it requires. And this tube is made something like a
telescope, so that if a heavy fall of rain should raise the level of the
water, all that the grub has to do is to push out another joint, when it
can breathe just as easily as before. This grub is often known as the
rat-tailed maggot.
HAWK-FLIES, ETC.
As you walk through a wood in summer, you may often see a black and
yellow fly hovering in mid-air. If you move, it darts away so swiftly
that the eye cannot follow its flight. But if you stop, and remain
perfectly still, it will come back again in a moment or two, and hover
just as before.
This is a hawk-fly, and it is very useful, for the mother insect always
lays her eggs on twigs and leaves which are swarming with aphides. On
these insects the grubs feed, so that as soon as they hatch out they
find themselves surrounded with prey, and destroy the little insects in
great numbers.
The house-fly and the bluebottle fly also belong to the order of the
_Diptera_. They are not very pleasant insects, but while they are
grubs they are really most useful, for they feed upon all sorts
of decaying substances. And another insect, called the flesh-fly, is
even more useful still, for it is the parent of from sixteen to twenty
thousand grubs: so that if even a single fly finds the carcass of a
small animal and leaves her eggs upon it, the little ones that soon
hatch out will devour it in a very short time. In a few days all these
grubs turn into perfect flies, and in their turn become the parents of
thousands of grubs: so that it has been said that three of these flies
could devour a dead ox as fast as a lion could!
The last insect that we can mention is a brown and gray fly known as the
warble. It is very troublesome indeed to cattle, for the mother fly lays
her eggs upon their backs. Then as soon as the grubs hatch, they burrow
underneath the skin of the poor animals, and form large swellings there,
in which they spend the whole of their lives. When they are fully fed
they wriggle out through a hole in the hide, drop to the ground, burrow
into it, and turn to chrysalids, from which the perfect flies appear a
few months later.