“We are going to look into the life of the caddis fly to-day; but before
I take them out of the water, I want you to tell me what you have noted
about them up to now.”
“They are always climbing up the water weeds,” said Frank.
“They are always adding to their cases,” said Tom.
“Some of them have died,” said Frank.
“What?” said his uncle. “Do you mean these at the bottom of the tank?
These are not dead, they are only asleep. Put your hand in, and take
some of these out.”
“Their cases are stuck to the pond weeds and to each other,” said Frank,
as he lifted a few out, and placed them in a saucer.
“Ah, I have it, Uncle George! They have gone into the pupa state. Is
that not so?”
Uncle George nodded.
“Look!” exclaimed Tom. “There are things like earwigs floating on the
water.”
“Never mind these just now, Tom,” said his uncle. “I am coming to them
by and by. Observe the wonderful cases which the caddis worms have made
for themselves.
“Here is one whose case, when we found him, was made of neatly cut
pieces of water rush. He has almost doubled the length of his case since
then; for see, the front half is made of cut stalks of water weed neatly
arranged.”
“He has got a fine collar of green pieces round his neck,” Frank
observed.
“Why are they always adding to the length of their cases?” asked Tom.
“Because they are always growing,” said Frank.
“That is the reason,” said Uncle George; “and they grow so fast that
they have actually to work hard at building.
“Observe those that make their cases out of tiny shells and stones. They
have made free use of the coloured beads and small pieces of coal which
we put in.”
“How do they manage to stick these things together?” asked Tom.
“A caddis worm is a busy creature,” his uncle replied. “He does two
things besides eating and growing. With those strong pincers, which you
see at his head, he saws off pieces of weed.
“Near his mouth he has got a kind of loom for spinning silk. These
pieces are stuck together with silk, which is a gluey substance when it
first comes from the creature’s body.
“These rough cases are lined with silk.”
“Why does he have to make a house for himself, and carry it about with
him?” said Frank.
In answer to this, his uncle took out a few of the active caddis worms,
and placed them in a saucer with water. He held one up.
“You see,” he said, “his case is open at both ends. Now, if I tried to
get him out from the front, I should never manage it. This is the way to
get him out.”
As he spoke, Uncle George pushed the head of a pin into the tail end of
the case, and the creature scrambled out at once.
“It is too bad turning you out of your cosy room, Mr Caddis,” Uncle
George observed; “but you’ll go back again as soon as you get the
chance, won’t you? I want my nephews to understand why you work so very
hard.
“Now, Frank, you can answer your own question, I think—‘Why does the
caddis worm build a house?’”
“Because he has a soft body.”
“Quite right. But why is he forced to protect his body?”
“Fishes would eat him.”
“Right again, Frank. If trout could speak, they might tell you that the
sweetest morsel in the stream is the caddis worm. Now, take your lens,
please, and tell me something about him.”
“His body is divided into rings, and there are the same number of them
as we found in the caterpillar.”
“Very good, Frank. Now give Tom a chance.”
“His head and the first three divisions of his body are hard cased. They
are black and yellow in colour.”
“He has six legs,” said Frank, “and they are attached to the first three
divisions of his body.”
“What about the last division of his body?” Uncle George asked.
“Oh, how funny!” said Frank. “It is divided into two large things like
horns.”
“These,” said his uncle, “are the hooks by which he fixes himself so
firmly in his case.”
“And what are all these curious big bristles for?” asked Tom. “They are
all over his body.”
“These are his breathing organs,” Uncle George answered. “The
caterpillar, if you remember, had breathing-holes along the sides of his
body. By moving his long body, the caddis worm causes a constant current
of water to pass through his dwelling.
“Look at the fourth segment of his body. How does it differ from the
others?”
“It is the broadest segment,” said Frank, “and there is a stout rounded
thing in the middle of it.”
“Yes,” his uncle replied, “and if we can get him turned on his back we
shall see two more of these stout outgrowths below, one on each side of
the same segment. This is really very clever. By it the animal keeps
himself in the middle, so that the current of water must flow all around
him.
“Now, look at the case of a sleeping caddis.”
“The front of the case is closed,” said Frank.
“How is it closed, Frank?”
“Well, there is a network of threads over it,” answered Frank.
“Yes; you see a caddis worm cannot do without fresh water, even when he
is asleep; so, before going to sleep, he builds a grating over the
entrance.
“When he wakes up, he has quite a new shape altogether. And this brings
us to those things which Tom said were like ‘earwigs.’ There are five of
them floating on the water, and two of these are dead. If you look, you
will find five empty caddis cases in the tank.”
“How does he get out of the case?” inquired Tom.
“Easily enough. Look at the strong pair of pincers he has got for
cutting his way through the silken grating with. No longer burdened with
his heavy case, he floats up to the surface. He crawls up out of the
water into the air.
“If there are no rushes or floating leaves about, he is sure to drown;
for your caddis is no longer a water insect, but a fly inside a thin
skin.
“Now, boys, I am going to show you something wonderful.”
Uncle George then took out the three living pupæ that were floating on
the water, and placed them on the table. The boys watched them for a
long time.
They were beginning to get impatient, when suddenly the skin of one of
the creatures burst along the back, and a lovely little fly, with brown,
gauzy wings and long feelers, came out.
After airing its wings for about a minute, it flew to the window. The
other two acted in just the same way.
“Now, my dear boys, I think you know something about the life of the
caddis fly. For a whole year of his life he is a crawling water insect,
then, for about a single day, he is a lively fly.”
“How does the caddis larva first get into the water?” asked Frank.
“As an egg, Frank. The female caddis fly lays her eggs in the water. She
sometimes even crawls down right into the water to lay them.
“A tiny caddis grub, no bigger than this pin-head, comes out of each
egg. As soon as he hatches out, he begins to build his case, to eat, and
to grow; and from the moment of his birth up to the closing up of his
tube, he is scarcely a moment idle.”
Exercises on Lesson XIV.
1. Turn a caddis worm out of his case in the way described in the
lesson. Place the insect in a saucer half filled with water,
and make a rough sketch of it.
2. When you have finished your sketch, place the empty caddis case in
the saucer, and watch how the creature gets into it.
3. Make two columns by drawing a line down the centre of a page of
your note-book. In the first column, describe the structure of
the caddis larva and fly; in the second, that of the cabbage
caterpillar and butterfly. Compare them.
4. In the same way describe the _mode of life_ of the caddis fly
(Column 1), and of the white butterfly (Column 2).
APPENDIX.
HINTS TO TEACHERS.
BUDS.—Twigs of beech, horse-chestnut, lilac, and hawthorn ought to be
taken in in December and placed in water. They should have as much
warmth and light as possible.
Willow twigs (for catkins) might also be forced in this way.
SEEDS.—Seeds should be soaked for twenty-four hours and then sown in
sawdust in boxes 4 inches deep. They should be sown in presence of the
pupils.
In winter these boxes should be kept on the hot pipes in school. The
sawdust should not be allowed to get dry, neither should it be deluged
with water, but kept evenly moist if possible.
Be careful to use water _not colder than the temperature of the room_ in
which the seeds are grown. Nothing checks growth more effectively than
chilling with icy-cold water. It is a good plan to keep the watering-pan
full of water near the hot pipes, refilling it always after use.
Seeds germinate best in the dark, but whenever the plumule shows above
the sawdust, the box containing them should be placed in the light.
Sufficient seeds should be sown at one time to supply a plant to each
pupil once a week for at least four weeks. A number of seeds or plants
should be dug up once a week and sketched by the children. Each sketch
should be compared with that of the previous week, and all changes duly
noted down.
The best seeds to grow are:—Broad bean, common or “large white” maize,
runner bean (“Painted Lady”), French bean, kitchen pea (“Stratagem”),
and white mustard.
A few seeds of white mustard should be sprinkled on a small piece of
moist blotting-paper, and covered over by a small glass bell-jar or an
inverted tumbler. In less than a week the root-hairs may be seen.
If hot-water pipes are available, the following seeds should be grown,
as their germination is interesting:—date stones, walnuts, chestnuts,
almonds, cherry stones, orange pips, seeds of cucumber and sunflower.
After maize and bean (or pea) plants have reached the height of 5
inches, they should be transferred to bottles of tap water—as described
at the end of Lesson VI.—and the continuous growth sketched and noted
from week to week.
POND AND DITCH HUNTING.—Make a ring of stout brass wire about 8 or 10
inches in diameter, and to this attach a bag net made of mosquito
netting not more than 9 inches deep. In making the wire ring, leave
attached to it about 5 inches of the twisted ends of the wire. Such a
net as this can be easily carried and quickly attached to the end of a
walking-stick by means of a piece of string.
The best “finds” are often made by sweeping the net under banks and
among pond weeds.
FROG SPAWN.—Frog spawn is abundant in ponds and ditches everywhere in
March. It should be kept immersed in as much water as possible in a
large vessel, preferably of glass. Whenever the water show signs of
fouling, it should be changed; but, as changing water containing
tadpoles is somewhat difficult, the fewer changes the better.
As in the case of seed growing, the development of the tadpole should be
learnt by weekly sketches and notes.
NEWTS.—Newts can be taken with the gauze-net or in the following
way:—Tie a piece of small worm on to the end of a cotton thread fastened
to the end of a willow or hazel switch. Cast into the part of the pond
where the newts are, and await results.
Live newts, fish, frog spawn, etc., may be obtained from Messrs Willson,
Live Stock Providers, 37 New Oxford Street, London; Thomas Bolton, 25
Balsall Heath Road, Birmingham, and other dealers. Newts should be fed
once a day on pieces of small worms.
CATERPILLARS.—Caterpillars and pupæ, if not obtainable in local woods,
fields, and gardens, can be had from Messrs Watkins & Doncaster, 36
Strand, London, and others.
CADDIS LARVÆ.—Caddis worms are to be found in almost every stream, pond,
and ditch. Most of them are vegetable feeders: therefore a plentiful
supply of water weeds should be placed in their tank. Carnivorous caddis
worms may be fed on small pieces of raw meat. (See Stickle-backs.)
STICKLE-BACKS.—Stickle-backs are common in canals and streams. They are
easily caught with the net. They should be fed once a day on grated
biscuit, and occasionally on raw meat. The meat should be chopped very
fine, and then pressed through a piece of perforated zinc. Very little
food suffices. If too much is put in, the residue should be removed by
means of a glass tube, as described in Lesson IX., p. 56. If no green
water plants are obtainable, the water should be changed at least every
second day by means of a siphon. Once a month is quite often enough if
sufficient green plants are kept in the tank and decaying matter
carefully removed. Do not over-stock—few fishes and much water is the
rule.
WATER PLANTS.—It is best to take the water plants which are found
growing locally. The following are fairly common:—_Elodea canadensis_,
water millfoil; _Potamogeton_ (_nitens_, _crispus_, or _filiformis_),
“water soldier”; _Vallisneria spiralis_, _Chara_, _Nitella_, water
star-wort and watercress. A good selection of excellent aquarium plants
are advertised at a cheap rate by the Solway Fishery Co., Dumfries.
Water plants, if not rooted in the tank, should be renewed occasionally.
LARVÆ CAGE.—Take four square pieces (about 1½ inches square) of wood,
each a foot long, and nail or screw them upright into the four corners
of a square piece of ¾-inch deal measuring a foot each way. Stretch
mosquito netting over sides, end, and top, arranging that one side can
be opened. This can be managed by fastening the last fold of netting to
one of the upright posts by three drawing-pins. Fresh leaves should be
supplied daily. For those caterpillars which pupate in the soil, a
shallow earthenware flower-pot—known in the trade as a “seed-pan”—should
be supplied. The seed-pan should be filled with soil, the pupæ placed on
the surface, and a layer of moss placed over them. Once a week the moss
should be dipped in water, squeezed almost dry, and replaced on the
pupæ.
AQUARIUM.—Procure from a local florist or seedsman what is known as a
“propagating bell.” These cost from 1s. up to 2s. 6d. A block of wood 12
inches square and 4 or 5 inches in thickness is also required. Bore a
hole about 2 inches in diameter right through the centre of the block,
to hold the knob of the bell. Then, with a gouge chisel, make a
saucer-shaped hollow round the hole, to roughly fit the rounded end of
the bell. Before fitting the bell into the block, interpose a thin layer
of moss.
This makes an excellent aquarium—elegant and serviceable. Keep the
aquarium in a window, but shade it from bright sunlight.