Here we are in the woods again.
How sweet it smells!
Let us sit down by this brook and look into it.
It is such a clear little stream, with fine sand and little pebbles at
the bottom.
What has Nell found that pleases her so?
She says she sees some little bars of sand moving about.
Ned says they are not sand bars but tubes of sand, containing a little
live thing.
The truth is, this sand bag is a house, and its occupant is a larva.
[Illustration]
See the black head come popping out, and the tiny fore legs.
The larva does not come entirely out, you see, but pulls its house along
with it, and when it is frightened it pops back into its little stone
case.
Mollie says it reminds her of a hermit crab.
A hermit crab, you know, lives on the seashore and takes possession of
an empty snail shell for a house.
It comes partly out dragging its house with it, but if you disturb it,
it draws back, sometimes quite out of sight.
[Illustration]
This little larva lives in a house, too, but it is a house of its own
making.
It is the larva of the caddice fly, or case fly.
Let us put one of these little sand cases in the saucer here.
Please fill the saucer about half full of water, John. Thank you.
Now, Mollie, I see you have picked up a fine big caddice case.
Put it in the saucer, and let us watch the larva crawl about.
[Illustration]
It never comes entirely out of the case, you see. It holds on to it with
the hinder part of its body.
Its little black head is hard, but its body is soft, and that is why it
does not like to expose itself to hungry larvæ that might be living in
the water.
May says she wants to see the whole larva.
Suppose we carefully break away the little sand case.
No, indeed, little Nell, we are not going to hurt the larva; we are only
going to open its house.
[Illustration]
There, the larva is outside now, and you can see what a tender, pale
little thing it is.
It does not like to have its soft body exposed.
See! it is already gathering little bits of sand together.
It seems to be sticking them fast to its body.
It is really binding them together by a saliva-like substance from its
mouth.
It draws out little glistening threads that harden into silk as soon as
they touch the water.
Queer saliva you think.
But the caddice larva does not find it queer. It is used to saliva that
hardens into silk.
Yes, that is the way the larva of the aphis lion and of the ant lion
made their cocoons. They spun out silk in this manner.
The caddice larva makes its house of silk and sand and also lines it
with a beautiful covering of fine silk.
Yes, May, it papers its walls with silk.
You see it did not hurt the caddice larva to take away its house; it
immediately went to work to build another.
Why not pull it out, instead of breaking its house to pieces?
Because if it had been pulled hard enough to come out, it might have
been torn to pieces, it is such a tender little thing, and it holds fast
so tightly.
So the best way to remove it safely is to break its case bit by bit from
around it.
It does no harm to break its case if one is careful. It will soon build
another.
Yes, this larva has no distinct thorax. It is like the larvæ of the
dobson, the aphis lion, and the ant lion in that respect.
[Illustration]
See! John has found one whose tube is made of quite large stones as
compared with this tube of fine sand that we have broken open.
Some caddice larvæ build houses of wood instead of stone. They stick
little twigs together, and some use little pieces of leaves.
Others again use tiny snail shells which, as you can imagine, make very
pretty cases.
[Illustration]
Our little caddice has made a neat little house of fine sand grains very
nicely put together.
Some others make much rougher houses.
You will be apt to find the caddice larvæ in any brook and in some
ponds, and I hope you will always look for them.
Notice the tracery in the soft mud of the brook.
Those lines that look as though some one had been ornamenting the bottom
of the brook are made by our caddice larvæ.
[Illustration]
They drag their cases along and thus make these lines.
Sometimes such lines are made by the little fresh-water snails; but you
can always find the decorator by following along the lines he makes.
What, May? How is the delicate larva able to cling to the case tightly
enough to pull it along? If you look at it very carefully, you will find
a pair of tiny hooks at the tail end by which it can hold on to the silk
lining; and some caddice larvæ have hard points on their backs which
help them to hold fast.
The caddice larvæ are carnivorous; that is, they eat animal food.
Yes, May, their food is usually the larvæ of other insects, but you will
be glad to know that some of them eat plants too.
They eat the larvæ of the May flies when they can find them and no doubt
they build these strong cases about themselves to prevent the May fly
larvæ from returning the compliment.
Frank has found some empty cases, yes, and some that are closed at both
ends.
Now, let us look at this one closed at both ends. What do you suppose is
in it?
We will open just one of these closed cases.
There! It is a pupa! Yes, Nell, a very pretty doll is this.
[Illustration]
It has a thorax, you see, and an abdomen. Its long antennæ lie close to
its body as do its little wing pads.
Yes, the caddice larva grows and moults in the usual way. It keeps
adding to its house as it grows longer. Finally, it closes the end of
its little tube and lies quite still.
You know what happens next. Its wormlike form divides into thorax and
abdomen. Legs and wings appear, attached to the thorax. In short, it is
no longer a wormlike creature.
Finally, it comes forth from its case. It never goes into it again.
[Illustration]
It does not need to, for now it is a dainty little nun, with a long,
tan-colored cloak. Its cloak, of course, is its wings folded down about
its body. Like the fairy May flies it has no mouth and eats nothing in
the adult form.
It looks like a dainty brown moth as it flutters about the bushes and
goes flying up and down the brook.
You will always find these little brown-cloaked figures flitting about
the brooks, where the caddice larvæ live.
You see the caddice undergoes a complete metamorphosis.
No, it does not belong to the Neuroptera.
Examine its wings very carefully. Look at them through the magnifying
glass, and you will see they are clothed with hairs.
So these are the hair wings.
The name of the order to which they belong is Trichoptera, from
_pteron_, a wing, and _thrix_, a hair.
Sometime you must take a caddice larva from its house and put it in a
saucer of water with fine bits of mica, which you know is another name
for the isinglass that makes the little windows in our stoves.
If you are fortunate, your caddice will build for itself a little glass
house, through whose walls you can look and see what is going on inside.
[Illustration]
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