The larvae of insects - and in a few cases the mature animals themselves - are interesting. The bottoms of most of our small ponds are alive with different species, some of which are very curious in their habits. It unfortunately happens, however, that the fish have a strong liking for them; and those for which the fish have not a strong liking have a strong liking for the fish, so that when we exclude both those that are easily destroyed and those that are destructive, the scope for choice is rather narrow. The water boatman (Notonecta glaucus) is a common inhabitant of ponds and puddles, and an interesting subject for the aquarium, and so is the whirligig (Gyritms natator). The larvae of the dragonfly and of the dytiscus are curious but destructive; and one of the most singular objects is the larvae of the Corydalus. It is known also as the "helgramite," and is largely used for bait by fishermen. The motion of its external gills, when watched under the microscope, is very curious. The large water-beetle (Hydrous piceus) is said by some to be harmless, but our experience does not bear this out.
But of all the insect inhabitants of the pond or tank, the caddis-worm is the most curious and wonderful. This curious insect builds a little house for itself, and carries it about on its back, - enlarging its dwelling as its body increases in bulk. These dwellings, or "cases" as they are called, are formed of sticks, stones, and other material, and are designed to afford protection to the animal while in its defenseless state. But it often happens that some trout or other voracious enemy comes along and swallows not only the poor cad, but his "castle" as well. As a still further protection, therefore, the caddis-worm endeavors to escape observation by forming his house as nearly as possible of the same color as his surroundings.