The widest swimmer - the largest and rarest beetle in Russian waters

Part of the beetles chose water rather than land for their habitat. One of the large families of aquatic beetles is the swimmers (Dytiscidae). It includes more than 4000 species of predatory beetles. Most of the medium and small sizes are painted in dark or yellowish colors. The widest swimmer looks like a real giant among relatives. Large water beetle is found in Europe and Western Siberia. The insect is very sensitive to pollution of water bodies, therefore, the number of species is reduced. The widest swimmer is listed in the regional Red Books of the Russian Federation, is protected in Ukraine, and is on the IUCN Red List.

The largest water beetle of Russia lives in the European part and Western Siberia. The common swimmer is found in Northern, Central and Eastern Europe. Insects are recorded in the forest-steppe zone of Ukraine, in Kazakhstan.

Morphological description of the species

The broadest or widest swimmer (Dytiscus latissimus) belongs to the winged wing order, the family and genus swimmers. The length of the imago is 35-45 mm. The body is oval, flattened. The lateral parts of the elytra are greatly expanded, they protrude on the sides in the form of sharp plates. Coloring is greenish-brown, dark brown or black. Pronotum and elytra bordered by yellow stripe. The lower body is yellow. A dark color with a green tint makes the beetle invisible to predators. The slightly convex streamlined body shape is adapted for movement in the water column.

Interesting fact. The Russian name of the bugs “swimmers” came from their excellent swimming qualities. The Latin name for the genus Dytiscus means “diving”.

The head, pronotum and elytra are closely fitted to each other. No protruding parts or corners. The head is partially pulled into the chest. Its width is greater than length. The eyes are convex, facet type. Antennae 11-segmented. There are yellow spots on the forehead. The oral organs consist of strong stings, maxillas, upper and lower lips. The front legs are short; they are adapted to hold prey and move along the stems of aquatic plants. The last segment of the tarsus ends in a claw.

The middle and hind limbs are used when swimming. The hind legs are elongated, with powerful hips and flat legs, the parts of which are triangular in shape. The limbs are covered with long setae. Swimmers have a pair of transparent wings. in a calm state they are hidden under the elytra. Used for flights to wintering places or to search for favorable habitats. The abdomen consists of 8 segments. The lower part is dense with chitinous cover, the upper soft is hidden by elytra. On top of each segment is a breathing hole.

Sexual dimorphism

The differences between male and female individuals are manifested in the elytra. In males they are smooth, and in females they are covered with longitudinal grooves. The front legs of the males have special devices to hold partners during mating under water.

Lifestyle & Reproduction

The wide swimmer inhabits stagnant or slowly flowing waters. For living, he needs a pond with a size of 0.1 hectares. Vegetation should be well developed in the reservoir. Swimmers are active predators, feed on insects, mainly caddis flies. Attack fry and tadpoles.This species, due to its small number, does not harm fish farming. On land, beetles are selected in the evening. They simply cannot take off from the water.

Adults should lose weight by getting rid of intestinal contents. Then air is pumped into the tracheal system. Having raised the elytra, the swimmer is ready to take off. They fly in search of new sources of food, looking for the sparkle of water. The landing is sharp, without braking. The beetle goes under water and immediately tries to sink closer to the bottom.

Information. A wide swimmer lives in water bodies with a high oxygen content. Its presence serves as an indicator of the cleanliness of a pond or lake.

Propagation Features

In the life cycle of the broadest swimmer there are two periods of mating and breeding. The first, more intense, falls at the beginning of autumn - September and October. Young adults who have just left pupation tend to continue the genus. Less often, mating occurs in early spring. During copulation, the male with its front legs with suction cups is pressed against the female’s flap, and the middle clings to the elytra. such a tandem swims for about two days.

Insects periodically pop up for breathing. The male on top exposes the end of the abdomen and normally receives oxygen. The female’s abdomen does not reach the surface, it releases an air bubble from under the elytra and breathes due to the diffusion of oxygen from the water.

Interesting fact. The female, weakened by a lack of oxygen, for some time cannot independently be kept on the surface, her partner supports her.

Mating ends when the male transfers his spermatophore to the female’s copulative bag. Fertilized individuals have a special sign in the form of a white mass on the eighth segment of the abdomen. They remain to winter. Egg laying begins next spring. Beetles wait until the ice melts in the pond and the vegetation revives. In March-April, the female lays eggs on the stems and leaves of aquatic plants. Through an incision made by a sharp ovipositor, eggs enter the plant tissue. The masonry stretches until June. During this period, the female manages to lay 500-1000 eggs. The time of embryonic development depends on temperature. On average, it takes 9-40 days.

Larval development

Outwardly, the larvae are completely unlike their parents. They have an elongated abdomen, a heart-shaped head, and crescent-shaped upper jaws. Has two pairs of simple ocelli, antennae with 6 segments. Three pairs of swimming legs are attached to the chest, all segments of which have long hairs. Abdomen of 8 segments, two short appendages at the end. At the base of the caudal appendages are spiracles. The larva spends the main part of life in water. She swims well, preys on smaller larvae. For breathing, it emerges vertically to the surface and exposes the tip of the abdomen.

The offspring of swimmers hunt from an ambush, grabbing floating prey of a suitable size. The larva responds to any movement. She does not have a mouth gap, channels pass through the sharp jaws for injecting poisonous enzymes and then sucking out a liquid nourishing cocktail. The larva replaces three ages, molts twice, dropping a tight skin. At the last age, its size is 50-60 mm. For pupation is selected ashore.

The larva looks for a depression under the stone and builds a cradle. The doll is hiding in a round hole under the earthen dome. This is the only land phase of the broadest swimmer. It lasts 2-4 weeks. Young adults appear in the fall. After leaving the cradle, they have soft integuments. Beetles need a week to cover with chitin.

Limiting factors and species protection

The wide swimmer is listed in the IUCN Red List as a threatened species. Insects died out in several European countries: France, Germany, Belgium, the Netherlands. Limiting factors: drainage and pollution of water bodies, destruction of the coastal zone. A rare species fell into several regional Red Books of Russia. Water beetles under protection in the Voronezh, Lipetsk, Ulyanovsk, Belgorod region.