Edward F. Bigelow, « Insect Carpenters and Masons ». Popular Science Monthly, New York, D. Appleton, juillet, 1916, pp. 95-96.
The young naturalist who lies face downward at the brookside, and with shaded eyes watches the busy life that there has its being, will see, in many places, little masses of small stones or bundles of small sticks, moving on the bottom of quiet pools as though they were alive. When out of the water they seem to be only groups of stones or clusters of sticks, motionless and dead. But they are the homes of living larvae. By putting them in water or by pulling them apart, a whitish habitant is discovered-a larva which is a dainty morsel much relished by fish. Nature has provided it with an ingenious means of protection. The little caddis fly larva is an exemplification of the old saying that « necessity is the mother of invention, » since the little animal does not always build as his ancestors built but adapts himself to the circumstances of a new environment and utilizes whatever material may be available. In some localities the cases are made of stones ; in others of short twigs ; in still others, some of the little builders and mechanics bore out the interior of a slender twig or straw and use the hollow as a protection against the enemy fish.
When caddis flies are placed in small aquaria they extend the body out of the front of the protecting case and carry it as they crawl. But jar the receptacle and the larva instantly retreats into its house. It is hardly possible to pull the little creature out of its case, except possibly from the smooth straw. It clings to its covering with peculiar tenacity by means of two hooks at the rear extremity of the body. So firmly is it anchored to the sticks that violence will not dislodge it, unless the force is sufficiently great to pull the insect in two.
But the larva may be driven out by using a tiny toothpick with a blunt end, or by anything else of the kind that does not terminate in a sharp point. Push this into the rear of the case and the little animal at once unhooks himself and hasters out to find a new home.
Usually the cases are straight but sometimes they are curved, and a few spiral forms have been found, which closely resemble minute snail-shells. ../… In some places empty cases may be seen at the edge of the brook. Often they almost completely cover the rocks and the earth between them. In such instances the insects have emerged at the time of a freshet and the retreating water has left the cases stranded high and dry. The two empty cases here illustrated were obtained in this manner. They were selected from a large number because they are perfect examples of what the mason calls ashlar work, that perfect fitting together of stones without packing. Common as are the caddis worms and as often as they have been observed, not a single one has had its life history recorded in this country. A fascinating field for original investigation is here open to the first comer. Endeavor along this line is sure to be interesting.