Clifford Bennett Moore, The Book of Wild Pets: Being a Discussion on the Care and Feeding of Our Native Wildlife in Captivity, Boston, O. T. Branford & Co., 1954, pp. 86-88.
Caddis flies are best know by the gill-breathing larvae which we call caddis worms or sometimes « stick-worms », most of which inhabit our brooks and ponds and fashion cases within which they live. The majority of species build their cases by cementing together with their own saliva bits of foreign material. The interesting thing about these cases it that each species has a characteristic choice of material or a very definite style of architecture. The choice of material is, naturally, limited to the things found in the particular aquatic environment which the larva inhabits : vegetable matter such as particles of dead leaves, and harder unchewable substances like small pebbles, sand, and snail-shells. When a caddis-larva outgrows its case it sometimes squirms out and makes a new one, selecting the same materials and building according to the same pattern, but it generally enlarges its original case by simply building along the front edges. Within the case the larva sbugly lives crawling about by extending its head and thorax out of the front end so that its feed can be used, and dragging the case along. When full-grown the larva forms a sort of lid or door grating across the front opening of its case, though not complete enough to prevent water from entering ans supplying the insect with the oxygen it requires. After pupation in its case the adult swims to the surface and grasps some objects, from which it takes flight.
What would a caddis larva do when deprived of materials for case building ? Here is room for experimentation with your caddis larvae in which uou might dispossess them of natural case building materials, furnish them with other materials and see how they make out. Larvae deprived of their cases have been given bits of mica by some experimenters. One investigator, Ostwald, got larvae to build with a great variety of substances. The pond-dwelling caddis larvae are, for the most part, vegetarians and, if given vegetable matter for food, practically all, even so-called masons, use it for making cases. It may be possible, as Lutz suggest, that by starving them sufficiently and then giving them only exceedingly small pieces of food at a time, they could be forced to go without shelter rather than go hungry.
From Lutz’s account of his very original experiments dealing with flexibility in the case-making behaviour of larvae, we quote : « …four log-cabin builders were dispossessed of their cases and put into an aquarium with notjing but water and sea-sand with a little alga for food. This experiment was being carried on at the Mount Desert Island Biological Laboratory and the available sea-sand was made up largely of fine pieces of broken shells and sea-urchin spines ; one used some of these, but mostly alga ; and two were still naked. The following day three had shell and spine cases, the alga that one had used having apparently been worn or eaten off, and one still had no case, but there were two partly made and then abandoned cases in the aquarium.
« The material normally used by the larvae which build the log-cabin type of case consists of more or less cylindrical pieces of soft, partly decayed twigs or, in this Maine locality, of spruce needles which had fallen into the water. These are placed very definitely in a transverse position, with reference to the larva’s body. When I put the sea-sand into the aquarium, I did not notice that it contained a small amount of sea-urchin spines. It was, therefore, a matter of considerable interest that the larvae sorted over the sand and picked up here and there for use such a large proportion of the relatively rare objects which came nearest to being the shape of their normal material. That this was not because they could not use the flat pieces of broken shell is shown by the fact that they did use a few of such pieces and, in the case of one larva, it started with the exceedingly thin and flexible strands of alga, although it later changed to sea-urchin spines and some broken shell.
« This seeming exercise of choice, a possible evidence of real mental preference, was further illustrated in another experiment in which dispossessed log- cabin builders were first put into an aquarium with nothing but water and Utricularia, a delicate plant bearing curious »bladders » or pockets which entrap microscopic organisms. Nearly all of the larvae rather quickly made cases out of pieces of the plant which they bit off….
Be that as it may, the log-cabin builders in their Utricularia cases did not live peacefully together. One would come up behind another and steal a bit of plant from the case of the second in order either to eat it or to add that already-cut piece to its own case instead of cutting another piece for itself. After allowing this shifting of material from the rear end of one case to the front end of another to go on for a day or two, I put sea sand into the aquarium. Each larva had at that time a reasonably good, although rather short, Utricularia case. However, each began picking up sea-urchin spines. « Possibly the scarcity- of broken shell in these cases, as contrasted with those made by naked larvae which started with nothing but sea- sand and a little alga, is to be explained by the fact that these larvae already had fairly satisfactory cases and, so, made a more leisurely and careful selection of material. I quite realize the danger of such a suggestion with its implication that larvae of lowly creatures think. Possibly the preference shown for spines over broken shell may have a purely mechanical explanation in the shape of the tarsal claws with which the building material is handled… »
Caddis larvae of the genus Hydropsyche construct cup-shaped nets which always open upstream in the crevices or on the edges of rocks in waterfalls and riffles. The larvae remain close by in a loosely woven tubular affair keeping Watch and where they can easily reach the food which the water brings into the net. When full-grown the larvae make cases of sand grains, attached to submerged rocks in which they pupate. They later emerge as slender moth-like flies. The length of a larva is usually about half an inch. Hydropsyche larvae can be found together with their nets in brooks during both summer and winter, and they may be removed from such natural locations together with their tube-cases by means of forceps or a kniffe blade and transferred to small aquaria whose water is aerated by mechanical pumps or to a trough such as that devised by Needham (Fig. 53). In the trough with its running water you can get some new clean nets « made to order ». The making of a trough is a small job for the manual training shop. The materials needed are : (a) a piece of wire cloth 2 ‘’ x 3’’, (b) two pieces of flooring or other stuff, groove on one edge and two feet long, (c) two strips of equal length for the sides, and (d) a short cross strip for the intakes end.
« Makes as follow : Nail the two groove strips together to form the bottom. Saw a cross-groove near one end to reveive the screen. Place the screen in this groove, bending the ends flat against the sides of the bottom pieces. Nail on the two side pieces so that they will stand an inch higher then the bottom. Nail the short strip across the intake end (the end opposite the screen) in position, projecting both above and below the trough ; below, far enough to give a slant to the trough of about an inch per running foot. If the bottom be painted black Inside and dried before use, the nets made in this trough will show up better. »
A slight and continuous flow of water will need to be kept up in the trough. It is desirable to have the faucet as far from the trough as possible so that the water in dripping may become well aerated.