Probably, many have observed such a picture when a large dark-colored beetle rises from the depths of the reservoir with an oval body bordered by a yellow stripe along the chest plates and elytra. This is an insect belonging to the family of aquatic order winged beetles, a swimming beetle. The photo shows how bright and attractive it happens.
In the world there are more than four thousand species, and in Russia - about three hundred species in fourteen territories. Diving beetles inhabit deep water bodies with stagnant water, rich vegetation and animals. The swimmer is a predator. Ponds with a meager population will not be able to provide bugs with an adequate supply of food. Since the swimmer is the most insatiable water predator, it is not limited to eating small aquatic animals, sometimes it attacks fish and newts. It can attack animals, the size of which is larger than himself.
The beetle itself is unattractive for predatory animals, as it has impressive arguments against those who want to profit from them. In case of danger, the swimmer from under the chest shield releases a fountain of whitish caustic fluid, in addition, the color helps him. For waterfowl, the beetle is hardly noticeable.
Periodically, a swimming beetle emerges from the water, exposing the back of its body, and freezes in this position for some time. Why does he write such somersaults? The fact is that his respiratory system is arranged in such a way that oxygen enters through the spiracle located at the end of the abdomen. During the ascent to the surface, the air valve opens, and so the beetle receives a portion of oxygen. Soon, the swimmer again plunges into the water, taking with him a bubble of air under the elytra. The bug needs it not so much as a supply of air, but as a hydrostatic device. Having spent oxygen reserve, the swimmer again rises to the surface of the water. As a rule, a swimming beetle emerges every eight minutes.
Since the body of the beetle is lighter than water, the swimmer floats to the surface without any effort (water simply pushes it out), but immersion requires considerable effort and intense movement. To stay under water, the beetle is forced to cling to any water objects - algae, sticks, stones and so on. His forelimbs, equipped with sharp hooks, help him catch on.
Males have sucker discs on the front pair of limbs. They help to attach to objects with a smooth surface, and also serve as a kind of device to capture the female during mating. It is believed that these suction cups work with a sticky, water-insoluble liquid. Females do not have suction cups, therefore, their elytra have a greater number of furrows, although females are sometimes found with smooth elytra.
Thanks to well-developed wings, the beetle is able to leave its body of water and fly deep into the land for considerable distances. Diving beetle, this is a fairly powerful insect. In the water, an oar-shaped, posterior pair of limbs helps him move with hairs. Like a rower, a swimmer overcomes the density of water and sometimes develops a speed at which it is able to move faster than some fish.
Drilling holes in plants, the female lays eggs from which larvae emerge, and at the end of her development, the larva crawls out to land and pupates. A few weeks later, a swimming beetle emerges from the pupa, returns to the water, and life continues.