Hogs destroy many larvæ by rooting in the soil to find them for food.
CRAYFISH
Search for the crayfish in streams and ponds. Why is the crayfish hard to find? Hard to capture?
Obtain a living crayfish from a pond or stream and place it in a jar of water or in an aquarium.
The crayfish should not be placed in an aquarium containing insects and small fish which are to be kept, as it is fierce and voracious.
The pupils should study the living animal, noting its habit of lurking under stones; the sweeping of the water with the feelers; the backward movement in swimming, produced by bending the tail sharply underneath the body; the walking by means of four pairs of legs, the great claws being used to turn the animal; the use of the great claws in seizing prey and holding food near the mouth; the movements of the small appendages under the front part of the animal and the water currents caused by these; the movements of the small appendages under the abdomen of the animal.
FRESHWATER MUSSEL
The freshwater mussel—"clam" as it is usually called by school-boys—may be found in almost any stream.
Place a mussel in the aquarium, and note the opening and closing of the valves of the shell; the hinge connecting the valves; the foot protruding from the shell; the movements by means of the foot; the mantle lobes lining the shell and visible at the open margins; the two siphons at the rear of the animal—water currents may be observed entering the upper and emerging from the lower of these. Infer uses for these currents. Touch the edge of the upper siphon and observe how quickly the shell is closed.
Compare the mussel with the snail as to movements and shell.