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The caddis fly larva does not have teeth. He crushes his food between his jaws, the ends of which are notched. Both jaws move. They work sidewise instead of up and down. The caddis worm also has an upper and lower lip which move, and are made of the same hard material as his jaws.
The larva would outgrow his case if he did not make it larger. He usually does this by adding new material to the front of it.
Not all caddis worms use sticks for building material. You may find cases made of leaves, sand, or small pebbles.
Some caddis fly larvae do not travel about in search of food, but spin nets, and lie in wait to eat the food which is caught in them. Others attach their cases to rocks in running water and take food from the water which flows past.
One of the pictures which illustrates this chapter shows a number of caddis worm cases. One interesting case which is not shown, but which you will often find, is made of fir or pine needles. You can tell which is the front of the case, even though the caddis worm may have withdrawn into it, because the fresh needles are usually green, though the old ones have turned brown. If you find a caddis worm out of his case, you can put him in a jar by himself, and select his building material for him. Some caddis worms will even make cases of
small, colored beads, if that is the only material at hand.
The caddis fly larva is active for many
days. Finally he builds a screen across the ends of his case and remains quiet for a long time. This screen lets the water go through his case, but it helps to keep out dirt and other enemies.
During the resting stage in his life the caddis worm is called a pupa. Many interesting changes now take place in his body. Antennae grow on his head. Two pads form on his back. Wings grow inside these pads. A pupa also develops mouthparts which are different from those of a larva. The new jaws are long and pointed.
After a time the pupa cuts his way out of the case and swims to the surface of the water. There he sheds his pupal skin and spreads his wings in the sunshine
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