A beetle has two pairs of wings.
One pair is hard and bright.
It covers up the other pair
And hides them out of sight.
We see the straight line down his back,
And say: "A beetle. Quite!"
YOU will notice that the bodies of adult water beetles are more "streamlined" than those of the common land beetles. They are boat-shaped, and smooth, and the hind legs are flattened, so that they are particularly suited to life in the water.
Since beetles undergo complete metamorphosis, the young water beetle is called a larva. Larvae of water beetles are somewhat different in shape, but each usually has a broad, flat head, a thorax to which six
legs are attached, biting mouthparts, and a segmented abdomen. A few have gills; the others breathe air at the water's surface.
There are several kinds of diving beetles, whose larvae have somewhat different habits. The most common larvae of this group breathe at the surface of the water. When they need oxygen, they swim near the surface and poke their tails out of the water, taking in air through two breathing tubes at the ends of their long bodies.
Diving beetle larvae are more common and more noticeable than many others, and are usually among the first fresh-water animals to be collected. A diving beetle larva is a very fierce animal. He is sometimes called a water tiger. With his large, powerful jaws, he attacks and eats many animals as large as himself, or larger. Do not place one in a jar with other animals when you are collecting. At the end of your trip you are likely to find that you have a fat beetle larva, but many other animals have disappeared! A large larva will even eat his smaller brothers and sisters, or fight with another beetle larva of his own size until one has killed the other. His jaws have grooves through which he sucks the juices of his victims. He does not have a jointed beak like that of a water bug.
Watch one of the adults of the same group when he comes to the surface. He hangs there, upside down, with the tip of his abdomen just out of the water. Do you see him lift his wing covers slightly, taking in air under them? The air enters small openings along the sides of his abdomen and is carried through his body in fine, branched airtubes. He swims toward the bottom of the aquarium in search of food, until he has used his supply of air. Then he returns to the surface for more. His food as an adult diving beetle is much the same as that of the larva from which he developed.