Almost everyone who rested on the shore of a lake or river met a swimming beetle. This agile insect is a merciless predator and attacks many river creatures. These beetles do not show aggression towards humans, but if they feel threatened, they can bite. The bite of a swimmer is not dangerous to human life, but quite painful.
Origin of the species and description
The swimming beetle is a representative of the family of aquatic insects from the numerous order Coleoptera. In total, there are about 4000 species of these creatures, 300 of them are found on the territory of Russia. The Latin name of the beetle Dytiscus is translated as “diving”. The oldest fossil of this insect was found in Kazakhstan and it belongs to the Jurassic period.
Video: Swimming beetle
From the variety of swimmers, here are some of the most interesting species to study:
- banded beetle — the most common and largest. Its body is painted black with a characteristic orange border, the legs are also very bright;
- wide swimmer beetle — its main feature is that the larvae are larger than adults and can grow up to 6 cm in length; from dark brown to black with a greenish tint. In some countries, it is listed in the Red Book;
- garnet or phalarope — is small in size, quite common in Russia;
- diving — the smallest representative of swimming beetles. There is a swamp dive and a flat one. The body of the first is covered with stiff hairs.
An interesting fact: Swimming larvae digest food outside their body with the help of a special poisonous fluid that is injected into the victim. The larvae suck the nutrients out of it already in a fully digested form.
Appearance and features
The size of adult swimmers, color may vary depending on the species. The body length of the smallest specimens does not exceed 3-4 mm, large specimens reach 4.5-5.5 cm. The adult body is oval and flat, which is ideal for movement under water. The hind limbs have well developed muscles. The flattened legs and hind legs are covered with elastic hairs. The very method of movement in the water column is similar to rowing with oars. The front, middle legs of the bug are much shorter than the hind legs.
The body of a swimmer consists of three parts: head, breast, abdomen. The head is fixed on the chest, motionless and passes to the abdomen without clear boundaries. On the sides of a wide and flat head are rather large eyes, and each of them consists of 9000 ordinary eyes, thanks to which the insect is able to clearly distinguish between moving, static objects. The abdomen of the beetle consists of eight segments, which are protected by hard elytra.
The powerful jaw is located behind the upper lip. The mouth apparatus of the gnawing type, the jaw is designed for capture and quick chewing. The olfactory organ is a segmented long mustache of 11 segments. Swimmers breathe with the help of special holes located on the belly. A complex tracheal system radiates from the spiracles, and there are air sacs in the chest. By unclenching and squeezing the abdomen, the swimmer creates air movement in the trachea.
The color of the body of the swimmer larvae is brown, yellow, gray, sometimes the body is covered with a pattern. Young beetles are very similar to scorpions. Their head is flattened, the breast consists of three segments, and the belly of 8 segments. There is no mouth opening, and food enters through the jaw. The wide body gradually narrows towards the posterior end, which contains cerci, spines and setae.
Where does the water beetle live?
Swimmers are widely distributed throughout the world, they are found in Europe, Asia, on a vast territory from Sakhalin to the Atlantic Ocean, northern Africa. Swimming beetles prefer fresh water bodies of water, where the current is completely absent or it is very weak. They are found in abundance in ponds with stagnant, blooming water, swamps.
Most of the time the beetle spends under water, but can also fly — if necessary, insects overcome tens of kilometers. Most often, such flights of beetles are forced by the drying up of a reservoir or a small amount of food. Sometimes they can even fly into private pools, ponds, where ornamental and other fish are bred.
They are able to completely destroy fry and all other living creatures in an artificial reservoir. It can be quite difficult to drive them from their chosen place. In some cases, only the complete disinfection of the bottom of the reservoir and the re-breeding of its inhabitants can help.
Interesting fact: The swimmer bug takes root well even in aquariums. As food, meat can be used, which is pre-cut into small pieces. Be sure to cover the aquarium with a lid, as insects can easily fly away. Main condition — bugs cannot be placed in the same container as any fish.
What does the swimmer beetle eat?
Swimmers are fierce predators. Adults rarely feed on carrion, they are more attracted to live prey that will resist.
The main diet of swimmers:
- insects and their larvae, snails, tadpoles, fish fry;
- newts, frogs, small fish.
Algae beetles are not interested, they are completely carnivorous. If there are a lot of these insects in the reservoir, then in a short period of time they are able to destroy all the fish, attacking its fry in large groups. The beetles feel even a small drop of blood at a distance of tens of meters and immediately rush to this place. They look for food mainly only in the water column, they rarely go on land.
Interesting fact: Swimmers eat a lot. Sometimes they overeat so much that they are not even able to rise to the surface of the reservoir. In order to reduce body weight and emerge, the swimmer regurgitates everything recently eaten, completely empties the intestines and a special goiter. When there is algae nearby, it slowly rises to the surface of the reservoir along them.
The larvae of swimmers differ little from adults in their predatory instincts. They are able to attack rather large fish, it is very painful to bite if they fall into the hands of a person. Their jaws are incredibly sharp, similar to sabers.
Character and lifestyle features
The body of swimmers is lighter water and, if they are not overeaten, they very easily rise to the surface. It takes a lot of effort to get down. At the bottom of the reservoir, on the surface of the algae, the beetles are held with the help of special hooks on the forelimbs.
These insects actively hunt at night. If the living conditions in the reservoir do not satisfy them, then they go in search of another home and are able to travel long distances. Before starting the journey, the adult completely empties its intestines and then fills the air sacs. Only by removing all unnecessary as much as possible and reducing weight, the swimmer takes off. During a night flight, many beetles crash on the glossy surfaces of roofs and walls of buildings, as they take them for a body of water.
Most swimmers spend the winter in the soil or hide in cracks in the bark of trees. Some insects hibernate in the egg phase, others as larvae. Some adults remain in the water and actively swim until it freezes. When the ice sets, the insects burrow into the mud until spring.
Interesting fact: To replenish oxygen, the beetle floats to the surface and protrudes its abdomen above the water. An adult beetle should carry out such a procedure at least once every 15 minutes. Air is used by beetles not only for breathing, but also for controlling ascent and descent.
Social Structure and Reproduction
Immediately after hibernation, swimmers start breeding. Males do not care for females, they themselves choose a suitable individual and simply attack her, grabbing her with their front paws, and immediately start mating. The whole process takes place under water. At one time, the female can mate with several males, and some of them die from suffocation due to the lack of the opportunity to once again replenish air supplies. Males at this time are above the surface of the water.
After the mating process is completed, the females lay their eggs inside the algae, before piercing their tissues with the ovipositor. In one season, the female lays 1-1.5 thousand eggs. After 10-12 days, larvae appear. Depending on the weather, the process may take up to a month.
Swimmer larvae grow very quickly. They are excellent swimmers, able to breathe atmospheric air, like adults, but they expose the rear end of the body for this. The larvae, as well as adult beetles, are very voracious, they are merciless predators. Their first food: fish caviar, dragonfly larvae, caddisflies, mosquitoes.
With the onset of autumn, swimmer larvae leave water bodies and crawl ashore, where they build cradles for themselves from soil and plants. In such a shelter, they pupate. A month later, adults appear. At first they are white and soft like pupae, but after a few hours their surface hardens and darkens.
Natural enemies of the swimmer beetle
The imago of the swimming beetle lives on average 1-2 years. During their rather short life, these creatures are capable of causing great damage to the ecosystem of the reservoir, fish farms. If it were not for the natural enemies of the predatory beetle, then it would be very difficult to control its numbers.
The swimmer can be hunted by:
- large fish species;
- some birds, including all gulls;
- mammals that inhabit water bodies.
In case of danger, swimmers are able to quickly produce a special white secret with a pungent odor that repels some predators who decide to eat them. For this reason, there are not so many who want to attack her.
The rider insect is a natural enemy of predatory beetle larvae. Female riders purposefully look for larvae of swimmers by a special smell and lay their eggs inside their body, which then feed and pupate right inside the larvae. As they grow, the young swimmers die.
An interesting fact: The predatory beetle, despite its small size, is able to cope with prey that is three times larger than the predator itself. If one individual cannot cope with the victim, then other beetles rush to her aid — like piranhas, they just need to smell the blood in the water column.
Population and species status
In a number of African countries, the wide swimming beetle is under protection, as its number has sharply decreased due to changes in natural habitat conditions. On the territory of Europe and Russia, the reverse trend is observed – the population of the predatory beetle is being monitored in order to prevent a sharp increase in its number.
Swimmers in large quantities destroy fry of all kinds of fish, other insects and reptiles that are with them in the same reservoir, thereby disrupting the natural balance, causing great damage to fish farms. The danger of this beetle is also that it is able to fly long distances in search of a new home, when food in the old place becomes insufficient, thereby occupying new territories.
When natural enemies are not enough to control the number of predatory beetles , some species of fish that eat the larvae of swimmers can be launched into the reservoir. In extreme cases, special chemical compounds are used to treat the bottom from larvae, but this is applicable only in small artificial reservoirs. Sometimes it is enough just to equip a small fountain or waterfall, which will contribute to the movement of water, and the beetles will immediately leave this uncomfortable place for it.
The swimming beetle is a hunter. Nature has provided these creatures with everything necessary for this. They were known as cruel and fearless predators, they are often compared to flocks of piranhas, literally destroying everything in their path. Despite this, it is very interesting to watch them in their natural habitat, to follow their swift hunting.