Different waters hold their own special communities; the dainty glen stream shelters companies of mayflies in its swift riffles; pond shallows and meadow brooks are the homes of lurking dragonfly nymphs; and wayside puddles are populous with mosquito wrigglers and water-fleas.

In all these places living things must contend with winter cold and summer drought, with storms and flood waters. In winter the pond populations drop to the bottom, frogs and turtles dig under mud and broken plants, whirligig beetles hide under banks to come out with every warm spell, and fresh water sponges are packed in tough covered capsules. In summer when its own pool dries up the water boatman flies to some other pond but many caddis worms burrow into the mud bottom and endure the drought as best they can.