When these beetles wish to fly, they do not rise straight out of the water; they climb up the stem of some plant. Then, when they are high enough to make a good start, they spread their lovely wings, and skim away.
If you watch the ponds, you may see a water-beetle floating with his head down, and the tip of his tail stuck out of the water. What does he mean by that queer action?
He is getting air to breathe. Though he lives under the water, he breathes air, and he is filling up his diving-bell; or, rather, he is turning himself into a diving-bell. How does he do that? Let us see.
This beetle’s wing-covers are air-tight. The mouths of his breathing-tubes open under the wing-covers. When he has used all the fresh air he had, he wants some more. So he comes to the top of the water, turns his head down, and spreads out his feet to balance himself. Then, with a little jerk, he drives out any air that is yet under his wing-covers.
Then he draws in fresh air, shuts his wing-covers up close, and goes down with plenty of fresh, pure air to breathe.
I have known people who will shut themselves up in a room and breathe the same air over and over again.[19] The beetle, you see, is more sensible. He knows that if he is to keep his health and spirits, he must have good, fresh, clean air to breathe. So he takes all this trouble to get pure air.
FOOTNOTES:
[18] See Third Book.
[19] Let the teacher explain the evils of vitiated air.