Lesson LXXIX

The Gall-dwellers

Leading thought—The galls are protective habitations for the little insects which dwell within them. Each kind of insect makes its own peculiar gall on a certain species of plant, and no one understands just how this is done or why it is so.

Method—Ask the pupils to bring in as many of these galls as possible. Note that some have open doors and some are entirely closed. Cut open a gall and see what sorts of insects are found within it. Place each kind of gall in a tumbler or jar covered with cheesecloth and place where they may be under observation for perhaps several months; note what sort of winged insect comes from each.

Observations—1. On what plant or tree did this gall grow? Were there many like it? Did they grow upon the root, stem, leaf, flower, or fruit? If on the leaf, did they grow upon the petiole or the blade?

2. What is the shape of the little house? What is its color? Its size? Is it smooth or wrinkled on the outside? Is it covered with fuzz or with spines?

3. Open the gall; is there an insect within it? If so, where is it and how does it look? What is the appearance of the inside of the gall?

4. Is there a cell for the insect at the very center of the gall, or are there many such cells?

5. Has the house an open door? If so, does the door open above or below? Are there more than one insect in the galls with open doors? What sort of insect makes this kind of house?

6. Do you find any insects besides the original gall-maker within it? If so, what are they doing?

7. Of what use are these houses to their little inmates? How do they protect them from enemies? How do they furnish them with food?

8. Do the gall insects live all their lives within the galls or do they change to winged insects and come out into the world? If so, how do they get out?

9. How many kinds of galls can you find upon oaks? Upon goldenrod? Upon witch-hazel? Upon willow?

Supplementary reading—Outdoor Studies, Needham, pages 18 and 37; “Houses of Oak,” in Insect Stories, Kellogg; Manual for the Study of Insects.

A green little world
With me at its heart!
A house grown by magic,
Of a green stem, a part.

My walls give me food
And protect me from foes,
I eat at my leisure,
In safety repose.

My house hath no window,
’Tis dark as the night!
But I make me a door
And batten it tight.

And when my wings grow
I throw wide my door;
And to my green castle
I return nevermore.