“Oh yes,” said Frank. “Like the parent beetle, the larva comes often to the surface and hangs downwards with his tail exposed to the air. So these plumes must be his breathing organs.”
“And do these long, slender creatures actually become broad, stout beetles like the one we returned to the pond to-day?” Tom asked.
“Yes, Tom, they do. Just as your green caterpillar became a beautiful white butterfly. These larvæ hatched out of eggs which were laid by the female beetle in the stem of some water weed. She first cuts a slit in the water weed, and then places an egg in the slit.
“When the larvæ are full grown, they crawl out of the pond and bury themselves in ground. Here they pass the winter in the pupa stage. They come out in spring, fully-formed beetles, and pass the remainder of their lives in the water.”
“What are these curious creatures that crawl among the water weeds?” Frank asked. “They are very like the ‘slaters’ which we find among old wood-work in the garden.”
“That creature is the ‘water hog.’ Its proper name is Asellus, and it is very closely related to the garden ‘slater’ or wood-louse.
“These water hogs, like the whelks, are very useful in an aquarium. They eat up all waste matter, and so help greatly to keep the water fresh.
“By the by, I want you to watch the whelks from day to day. They usually lay their eggs in a clear, broad band on the inside of the glass tank; and with our lenses we can watch the changes in these eggs nicely.”
Exercises on Lesson X.
1. Procure some “water boatmen” from the nearest pond (see [Appendix]), feed them upon flies, and watch their habits. Notice particularly their method of swimming and of feeding. 2. We should not keep all our pond animals in one tank. Can you explain (giving examples) why this is? 3. Write the life-history of the diving beetle. 4. Make large sketches of the diving beetle and its larva. Compare them.