The Caddis Flies – Builders of Houses

Do I want to observe nature, my Father’s world, at its very best? An excellent method is to seat myself in some peaceful place and await quietly what may happen. There is no better place on a warm summer day than beside some glistening and rippling woodland pool. As we gaze into the depths of that pool our eyes notice a wide variety of objects. We will see last year’s leaves in various stages of decay, twigs and pieces of weeds are scattered about. As we watch we will notice movement. Strange, however, but the thing that seems to move is only a tiny cylinder of leaf particles which slowly moves along the bottom of the pool. As you wonder what propels this little cylinder along you notice a shining spot near one end of the cylinder. This shining spot is the head of a larva with six tiny legs close behind and is all that is visible of a representative of one of the most interesting of the insect orders. Safely protected inside its snug little home fastened together with its own spun silk is the soft succulent body of the caddis worm.
Other species of caddis fly larva are in the same pool. Each species is identifiable by the kind of house it builds. The “less industrious” simply cut off a hollow stem, into which the body snugly fits. When it has outgrown its quarters it moves to a slightly larger “prefabricated” dwelling and adds a little silk lining for comfort and protection.
Another species selects tiny pieces of weeds which to him must appear like giant logs and with these pieces the insect constructs a tiny cylindrical home. When this home is too small it simply slits open one side and inserts a new log.
Still another species builds a turret shaped home by crisscrossing the “logs” of its dwelling. These are but a few examples of the more than 3,600 species of the order Trichoptera. Each of these species is most easi8ly identifiable by the type of house each builds.

Some of them are remarkable species are the stone masons among the caddis flies. To locate these, we must go to a sandy or gravelly pool. If our eye has been properly trained to detect caddis-worm houses, dozens of styles can be found to attract our attention. Some of these larvae build just simple cylinders of very fine grains of sand. Others use small gravel. The caddis worms often pick up minute snail shells as they build their homes. Often the snail is still in the shell but off it goes as part of the caddis-worm home. If a big enough snail is involved and an opportunity is presented the snail to take hold of some substantial object of a true tug-of-war results. Sometimes the snail wins and manages to tear itself from the wall of the home. The caddis worm must then find another nugget to refill the gap in the wall.

The epitome of achievement in architectural design is reached by one species of caddis fly which, using fine sand grains and silk, builds a house in the exact shape of a snail shell.
The food of the caddis fly larva consists of tiny insects, algae and water vegetation. It is noteworthy that each species seems to restrict itself to one kind of food.

We do not wish our discussion to become laborious but before we leave the caddis fly larvae we should discuss a few more specialized forms. We find a rapidly flowing stream with water dashing over the rocks. Here we find the fishermen of the order Trichoptera. In the swiftest water, they spin a silken net. This is not a large web because that would be torn away but a small web about the size of a quarter. Some of these are flat webs but most are cup-shaped; a few are shaped like a funnel. In this web the larvae lie in wait for what the water may wash into their little trap.

What about the adult which must soon become an aerial creature?
Like most insects the larva when it is fully grown pupates. It closes itself in its case or web. At the proper time the pupa leaves its case and swims or crawls to the surface of the water. Here it molts and emerges as a fully winged caddis fly.
What does this insect look like?
The caddis fly is a moth like insect, covered with hairs and mottled in patterns of brown or grey, with very long, slender, segmented antennae. The antennae are usually as long as and frequently two or three times the length of the body. The legs are long and the insects make ready use of them by darting rapidly here and there when not in flight.
It ought to be observed that most species fly readily, although in a few the females are nearly wingless, and in others the rear pair of wings is greatly reduced in size. Although individuals do fly in the daytime, it is toward dusk or after darkness has settled down, on still, warm spring or summer evenings, that the individuals of the caddis species begin their wedding dance in great numbers over the quiet waters. At this time, when bright lights divert them from their dance, we are more likely to see them as they come to the windows of our homes.


Man was created as king under God over all creatures. Man as king also uses and has used the caddis fly and their larvae for bait in fresh water fishing. Man has even imitated this creature of God by modeling artificial lures after the adult caddis fly. The country boy, however, gets the most use from the caddis worms. He collects the little cases, which can be kept for several days, and then has a good supply of excellent bait on hand. When he is ready for fishing, the larva is extracted from the case to adorn his hook, or his bent pin.

Originally Published in:
Vol. 19 No. 6 August-September 1959