The swimmers are a large (more than 4 thousand species) family of aquatic beetles that live in almost all regions of the world, except the most arid. Some are able to live even under the ice.
Many of them are freshwater predators. The scientific name of the insect is Dytiscidae.
This term is derived from the ancient Greek word dytikos, meaning “one who loves to dive.”
From egg to pupa
Plyuntsy, like all beetles, inherent development with full transformation. This means that the insect passes through four stages in the process of life:
- imago (adult).
Females float eggs placed on the stems of plants that are located in the water.
These insects are quite prolific. In one clutch there may be hundreds of eggs.
Such clutches for the season, the female has time to do a lot. They have one of the largest eggs among beetles, they can be 0.5 cm or more in length.
Depending on the ambient temperature and the water body, the larvae leave the eggs after 1-6 weeks.
The larval stage lasts from several to ten weeks and depends on the feeding and temperature of the reservoir. For pupation, insects leave the water and dig a hole, moving over land with the help of jaws.
Adult beetles hatch from a pupa in 2-5 weeks.
The larvae of this species are bad neighbors for all the inhabitants of the reservoir and one of the most ferocious creatures in the ponds. They are figuratively called the tigers of the insect world. On the head of the larvae are large sickle-shaped jaws, capable of easily piercing the prey.
They are not intended for grinding food and biting, but they can be firmly attached to the victim.
The structure of the jaws of the larvae of the swimmer is much more complex than the powerful mites. Along the inner side of each chitinous mandible, channels leading into the oral cavity stretch.
These features of the oral apparatus are caused by extraintestinal digestion, the same as in many spiders.
Through the canals, the larva regurgitates a poisonous liquid from the esophagus to its prey that has a neuroparalytic effect. After the prey ceases to resist, the predator belches a new portion, but already with strong digestive properties. The latter is capable of destroying tissue to a liquefied mass.
Expanding and squeezing the pharynx, the larva of the beetle beetle, as if with a pump, sucks up everything that has succumbed to the action of its digestive juice. As soon as the meal was finished, the voracious larva was hungry again and immediately began to hunt.
Even a hundred tadpoles per day can not always saturate a predator.
Larvae and beetles attack water insects, tadpoles, newts and fry.
Despite the fact that the swimmer loses its gills in the larval stage, the imago is perfectly adapted for life in the reservoir. Small-sized beetles may not float to the surface for weeks using oxygen bubbles emitted by aquatic plants.
In addition, the insect is capable of stocking under the elytra.
Large representatives are forced to emerge more often, taking a characteristic position on the surface. They seem to hang on the mirror of water, sticking the back of the calf on the air. Oxygen penetrates the trachea, located under the rigid wings.
Suction air is necessary for beetles not only for breathing. It helps them balance the hydrostatic pressure at various depths.
For breathing under water, they take a supply of air under the sheaths.
In the rectum of the insect there is a special bag that helps it control the buoyancy and easily move from the aquatic environment to the air.. The method of its use is similar to the use of ballast in submarines.
Swallowing the liquid, the insect fills the bag, thereby allowing itself to easily overcome the surface tension of the water when immersed. Freeing the gut from the fluid, the beetle pops up.
Reaching the hard surface, he is ready to fly.
The swimmers are excellent flyers. For them, it is not difficult to change the place of residence in the absence of power or drying of the reservoir. The distribution of the species and the colonization of new ponds occur mainly by air.
Adults are not less carnivorous than larvae. Their diet:
- insect larvae;
- small fish and fry;
- other small inhabitants of reservoirs.
Beetles are endowed with complex glands located in the thoracic and abdominal regions. These organs release specific substances that the insect uses in various combinations.
The excreta have toxic, antimicrobial, fungicidal, water repellent and wetting properties. They help the insect to fight with parasites and confidently move in different habitats.
The life time of swimming beetles does not exceed one year; however, it can increase by 3-4 times if they live in an aquarium.
Adaptability to the aquatic lifestyle gives not so much the ability to “hang” on the surface of the water, as the legs of the swimmer. The latter resemble large oars.
In addition, unlike the legs of land beetles, the back pair of the swimmer is able to move synchronously. This allows the insect to accelerate sharply under water.
The remaining limbs are not less specialized: the first two pairs are perfectly adapted to capture and hold prey.
This beetle can be found in almost all habitable water bodies of Eurasia, the Americas, Australia, Africa and even the Antarctic. Outwardly, it seems to be quite harmless, but many species are able to secrete toxic secrets. There have been cases of successful beetle attacks on small birds and animals.
Therefore, we must remember that the swimmer is a predatory insect. Even if you really want to take a closer look, you should remember to be careful not to take it with your bare hands.
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