Lesson LXXXVI

The Caddis-worms and Caddis-flies

Leading thought—The caddis-worms build around themselves little houses out of bits of sticks, leaves or stones. They crawl about on the bottom of the pond or stream, protected from sight, and able to withdraw into their houses when attacked. The adult of the caddis-worm is a winged moth-like creature which comes in numbers to the light at night.

Method—With a dip-net the caddis-worms may be captured and then may be placed in the school aquarium. Duckweed and other water plants should be kept growing in the aquarium. The log cabin species is best for this study, because it lives in stagnant water and will therefore thrive in an aquarium.

Observations—1. Where do you find the caddis-worms? Can you see them easily on the bottom of the stream or pond? Why?

2. Of what are the caddis-worm houses made? How many kinds have you ever found? How many kinds of materials can you find on one case? Describe one as exactly as possible. Find an empty case and describe it inside. Why is it so smooth inside? How is it made so smooth? Are all the cases the same size?

3. What does the caddis-worm do when it wishes to walk around? What is the color of the head and the two segments back of it? What is the color of the body? Why is this difference of color between the head and body protective? Is the caddis-worm grown fast to its case, as the turtle is to its shell?

4. Note the legs. Which is the shorter pair? How many pairs? What is the use of the legs so much shorter than the others? If the caddis-worm case happens to be wrong side up, how does it turn over?

5. When it wishes to come to the surface or swim, what does the caddis-worm do? When reaching far out of its case does it ever lose its hold? How does it hold on? Pull the caddis-worm out of its case and see the hooks at the end of the body with which it holds fast.

6. How does the caddis-worm breathe? When it reaches far out of its case, note the breathing gills. Describe them. Can you see how many there are on the segments? How is the blood purified through these gills?

7. What are the caddis-worm’s enemies? How does it escape them? Touch one when it is walking, what does it do?

8. On top of the first segment of the abdomen is a tubercle. Do you suppose that this helps to hold the caddis-worm in its case?

9. What does the caddis-worm eat? Describe how it acts when eating.

10. How does the caddis-worm build its case? Watch one when it makes an addition to its case, and describe all that you can see.

11. Can you find any of the cases with the front and back doors closed? How are they closed? Open one and see if there is a pupa within it. Can you see the growing wings, antennæ and legs? Has it breathing filaments like the larva? Cover the aquarium with mosquito netting so as to get all the moths which emerge. See if you can discover how the pupa changes into a caddis-fly.

12. How does the caddis-fly fold its wings? What is the general shape of the insect when seen from the side with wings closed? What is the texture of the wings? How many wings are there? Which pair is the longer?

13. Describe the eyes. The antennæ. Does the caddis-fly walk on its toes, or on its complete foot?

14. Examine the moths which come around the lights at night in the spring and summer. Can you tell the caddis-flies from other insects? Do they dash into the light? Do they seem anxious to burn themselves?

Supplementary reading—“A Little Fisherman,” Ways of the Six-Footed, Comstock.

Little brook, so simple so unassuming—and yet how many things love thee!

Lo! Sun and Moon look down and glass themselves in thy waters.

And the trout balances itself hour-long against the stream, watching for its prey; or retires under a stone to rest.

And the water-rats nibble off the willow leaves and carry them below the wave to their nests—or sit on a dry stone to trim their whiskers.

And the May-fly practices for the millionth time the miracle of the resurrection, floating up an ungainly grub from the mud below, and in an instant, in the twinkling of an eye (even from the jaws of the baffled trout) emerging, an aerial fairy with pearl-green wings.

And the caddis-fly from its quaint disguise likewise emerges.

And the prick-eared earth-people, the rabbits, in the stillness of early morning play beside thee undisturbed, while the level sunbeams yet grope through the dewy grass.

And the squirrel on a tree-root—its tail stretched far behind—leans forward to kiss thee,

Little brook, for so many things love thee.

Edward Carpenter.