  Frank and Tom returned from the horse pond one day with their jars filled with curious creatures. “We took the water beetle back to the pond, Uncle George,” said Frank, “and I almost felt sorry to let such a cruel and greedy monster loose among the other creatures in the pond.” “You have here creatures even more cruel and greedy than the diving beetle,” said his uncle, looking into the glass jars which the boys had brought. “Here is the larva of the diving beetle, and a fiercer or greedier creature is not to be found in the whole world.” Uncle George refilled the three large tanks. He poured the contents of one of the jars into one of the tanks. It contained, besides the larvÆ he spoke of, a number of tadpoles, some small stickle-backs, and a great many water snails or whelks. In addition to these, there were one or two curious insects, with a pair of very long legs. They came to the surface every now and then, and moved their long limbs like oars. Whenever the tank was touched, they would suddenly dive to the bottom. Here they would remain for a short time, then, returning to the surface, would “oar” themselves along as usual. “What are these queer things, Uncle George?” Tom asked. “They look exactly like little boats.” “They are beetles,” Uncle George replied, “and they Just as Uncle George was speaking, a small fly alighted on the surface of the water. It was immediately seized by a water boatman, who dived with it to the bottom of the tank.
“That is how the creature feeds,” said Uncle George. “When an unlucky fly comes near, he seizes it with his two fore pairs of short legs, drives his cruel beak deep into its body, and dives with it to the bottom of the pool. When he has drowned his victim, he devours it at leisure. “But let us look at the creature I first spoke of—the larva of the diving beetle.” There were several in the tank. Uncle George lifted one out with a small gauze net. He placed it in a saucer of water and asked the boys to sketch it. “It has six legs,” said Frank. “Its head is large and flat, and there are two things like horns sticking out of it.” “These are the creature’s jaws,” said his uncle. Uncle George touched the creature’s head with the point of his pencil. Instantly the long, curved fangs moved apart, and the creature sprang at the pencil and closed its fangs upon the wood.
“What a fierce creature,” said Tom. “Yes,” replied his uncle. “We must remove the others from the tank, or there will be nothing left alive in it. See, one of them has caught a tadpole already.” And, sure enough, the creature had sunk his cruel pincers deep into the body of a tadpole. He shook the tadpole as a dog would shake a rat. “Those huge fangs are hollow,” Uncle George continued. “With them he sucks every drop of blood from “We shall have to put these larvÆ in a tank by themselves, and feed them upon pieces of fresh raw meat, to keep them from devouring one another. “Now, boys, I am going to describe this larva. Look closely, and see if I am right. You can correct your drawings as we go along. “His body, which is nearly two inches long, is narrow at each end and broad at the middle. It is divided into twelve segments, and to each of the first three of these segments a pair of legs are attached. His large, flat head is almost heart-shaped. At its broad end are a pair of large, beady eyes, three pairs of organs which look like feelers, and the two large, curved fangs with which he seizes his prey. “Notice how beautifully the legs are adapted for swimming. They are edged with long, stiff hairs, which stand out flat with every down stroke, but fold in when the legs move upwards. That is how the creature is such a graceful swimmer. “The last three segments of his body are thickly covered with long hairs. His tail is divided into two long plumes. You can see what these are for, I hope.” “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 “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.
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