Back swimmer

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Back swimmer
Common backstroke (Notonecta glauca)

Common backstroke ( Notonecta glauca )

Systematics
Class : Insects (Insecta)
Order : Schnabelkerfe (Hemiptera)
Subordination : Bed bugs (heteroptera)
Partial order : Water bugs (Nepomorpha)
Family : Back swimmer
Scientific name
Notonectidae
Latreille , 1802

Back swimmers (Notonectidae) are a family of aquatic insects in the suborder of the bedbugs (Heteroptera) within the suborder of the water bugs (Nepomorpha). About 350 species are known worldwide. The special feature of these animals is that they always swim with the belly side up - and that below the surface of the water. This noticeable swimming position results from the air supply carried along on the abdomen on the abdomen. Since they can sting sensitively, back swimmers are also popularly called "water bees" .

features

Back swimmers reach body lengths of around 13.5 to 18 millimeters. The top of the body is arched boat-shaped. The ventral side is always flattened. The air supply of the bedbugs is mainly on the belly side. Due to the positive buoyancy in the water, the underside of the animals turns upwards. The head is broad and has strikingly large eyes. The eyes are designed as so-called double eyes . The back ( dorsal ) and abdominal ( ventral ) parts differ in terms of the number of facets and pigmentation . The part facing the light is better organized and enables accurate vision. The side facing away from the light is less specialized and serves as a viewfinder with a wide field of view. The short feelers ( antennae ) of the back swimmers are on the underside of the head and rest on an air bubble, which is located in a pit between the head and fore chest ( prothorax ). The second and third links are hairy. The third antennae has special sensory hairs. The hair prevents the air bubble from beading off. The nerve lines of the sensory hair on the antennae convey muscle movements, which together with the air bubble that strives upwards act as an organ of equilibrium. Despite their aquatic way of life, the wings are very strong and fully developed. When the weather is warm enough, they crawl ashore, dry their wings (which can take up to 15 minutes) and fly, mainly to find new water holes. They plunge into this with closed wings. New water points can only be found with the help of the eyes, whereby they react to particularly bright surfaces. Back swimmers use their powerful rowing legs to move in gusts just below the surface of the water. The proboscis is short and strong.

Way of life

Common backstroke ( Notonecta glauca )
Common back swimmer (body top)

Back swimmers live in pools, ponds and on lake shores. The animals can also exist in large and deep rain puddles. They are adapted to life in water in a special way. Notonectids are agile swimmers. They are able to cut through the water through their laterally compressed body. The rear pair of legs is the rowing organ. The splint and the foot are covered with long, stiff, wettable ( hydrophilic ) bristle hairs. When the legs kick back, the bristle hairs spread and thus increase the oar area.

breathing

Spotted back swimmer ( Notonecta maculata )

To breathe, the back swimmer pierces the surface of the water with the tip of the abdomen in the supine position. The middle and front legs support the animal, which is lighter than water due to the air supply, against the surface tension of the water. The hind legs keep the balance. The tip of the abdomen protrudes from the water. This is surrounded by an unwettable ( hydrophobic ) ring of hair and can thus penetrate the surface membrane . When the abdomen is stretched out, two rows of tunnel-forming bristles open up on the abdomen and take in air. These close again when you descend. These supply channels communicate with cavities on the chest and under the wings. Back swimmers are literally surrounded by air spaces. At the bottom of these grooves there are tracheal openings so that oxygen from this supply can be used for breathing, i.e. it can diffuse into the trachea . This air supply makes the buoyancy so strong that you have to row hard with your hind legs or hold on with the two pairs of front legs.

nutrition

In the supine position, the animal remains below the surface to wait for prey, which either comes to the surface to breathe or swims by within reach. Notonectids can also absorb surface vibrations from insects that have fallen into the water. They move quickly towards the prey, grabbing it with the middle and forelegs, pulling it underwater and sucking it out. Almost all back swimmers are predators who feed on any insect that overwhelms them. Even small fish and tadpoles are grabbed and sucked out.

Outside of Europe there are species in the Notonectid family that feed on plankton . So Buenoa margaritacea is a plankton eater. The bug puts the front and middle legs close to the body. The hair on the thighs forms a kind of trap through which the water is filtered. Microorganisms stick to the bristles.

Reproduction and development

Juvenile back swimmer, 2–3 mm long. View from the ventral side.

The pairing of the back swimmers can take several hours. Therefore, they need to be in a position where they can breathe. They hang next to each other on the surface of the water. The male is slightly below the female. The laying of eggs is different depending on the species. Notonecta glauca lowers its elongated, oval, approximately 2 millimeter long eggs into plant tissue using a short laying tube. Notonecta obliqua and Notonecta lutea behave similarly . Notonecta viridis occasionally glues its eggs, Notonecta maculata always to stones. The times of oviposition are also species-specific. In Notonecta glauca , mating starts at the end of March and the eggs are laid soon after. Notonecta viridis extends the oviposition into autumn. Notonecta maculata does not begin to lay eggs until autumn and continues in the warm winter months. This results in different forms of overwintering of the back swimmer species as a full insect or as an egg.

Back swimmers, like all bedbugs, are hemimetabolic . They go through five larval stages that merge into one another via moults. The larvae gradually become more and more similar to the adult animal.

distribution

Back swimmers of the genus Notonecta are widespread and species-rich , especially in the Neotropics . While species of the genus Anisops are numerous in the south of the Old World, there are species of the genus Buenoa in the New World .

Systematics

Genera and species (selection)

Species in Europe

Web links

Commons : Back swimmers (Notonectidae)  - Collection of images, videos and audio files
Wiktionary: Back swimmer  - explanations of meanings, word origins, synonyms, translations

swell

literature

  • KHC Jordan: Water bugs. The New Brehm Library, Leipzig 1950.
  • Ekkehard Wachmann : watch bugs - get to know . J. Neumann - Neudamm, Melsungen 1989, ISBN 3-7888-0554-4 :
  • E. Wachmann, A. Melber & J. Deckert: Bugs. Volume 1: Dipsocoromorpha, Nepomorpha, Gerromorpha, Leptopodomorpha, Cimicomorpha (part 1) revision of the bugs in Germany, Austria and German-speaking Switzerland. Goecke & Evers, Keltern 2006, pp. 51–57. ISBN 3-931374-49-1 .

Web sources