Tumbler beetle

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Tumbler beetle
Tumbler beetle

Tumbler beetle

Systematics
Trunk : Arthropod (arthropoda)
Superclass : Six-footed (Hexapoda)
Class : Insects (Insecta)
Order : Beetle (Coleoptera)
Subordination : Adephaga
Family : Tumbler beetle
Scientific name
Gyrinidae
Latreille , 1810

The tumbler beetles , also rotary beetles or gyroscopic beetles (Gyrinidae), are a family of beetles . They live on the surface of bodies of water, where they swim around in extremely fast circular or spiral movements.

features

Tumbler beetles are 3.5 to 8 millimeter long, oval, mostly shiny black beetles with a head sunk into the chest section (closed body contour) and a black, yellow-red or red-brown underside.

It is characterized by the short, pin-shaped antennae, the long front legs and the short, widened middle and rear legs. The rear legs are greatly widened, flattened and can be folded up like a pocket knife, and they have strong bristles.

The complex eyes of the wobble beetle are divided into an upper and a lower half. Air and water have a different index of refraction . The eye parts were created as an adaptation to this. Their structure means that they are adapted to the respective medium and sharply separated from one another. This allows the beetle to swim on the surface of the water to observe its surroundings both underwater and in the air.

Way of life

A group of tumble beetles on the surface of a small canal

Tumbler beetles are the only beetles that colonize the water surface ( Neuston ). The animals often live gregariously (swarming, often several hundred, even several species) on the surface (body cannot be wetted) of stagnant and moderately flowing water, where they prey on insects living on the water or who have died or dive for food.

The beetles move rapidly in circles at speeds of up to 50 centimeters per second, especially when the sun is shining, and are good fliers. Due to the closed body shape (low water resistance), but above all due to the design of the two rear pairs of legs as rowing legs, they are perfectly adapted to movement in the water. All parts of the legs are flat and the first phalanges are widened on one side. The splint and the fourth phalanx are covered with flat, articulated bristles, which automatically and at lightning speed expand when the oar stroke begins due to the counterpressure of the water. When the legs are pulled forward into the starting position, these parts slide into one another like a fan, the leg is rotated and moved with the narrow edge forward. The rear pair of legs, which has a particularly large number of platelet-shaped bristles, acts as the “main rudder” with a beat frequency of around 50 to 60 beats per second (the middle pair of legs is only about half as fast). The rowing apparatus of the wobble beetle is more efficient than comparable organ systems in any other known aquatic insect. More than 84 percent of the energy used is converted into feed, while the paddle wheel of a steamship, for example, only achieves an efficiency of 55 percent. The undirected "tumbling" movement of the beetles on the water is caused by their inability to move the row legs on both sides completely simultaneously. On land, the beetle can only move very awkwardly because of its highly specialized swimming legs.

Due to their completely different construction, the pair of forelegs is not suitable for swimming - it serves as a grasping organ (prey, copulation, holding on under water). The front tarsi of the male are, as in the males of other water beetle families, widened and provided with numerous suction cups (copulation aid).

The tumbler beetle Gyrinus japonicus

When swimming in circles, the tumbler beetles perceive the finest vibrations on the surface of the water with the help of a highly sensitive organ located in the second link of the short, powerful antennae for registering vibrations, the Johnston organ . This sensory organ enables the animals to avoid collisions and to locate prey and conspecifics. In the experiment, tumble beetles were able to swim through a wire mesh screen without bumping into them, even though the meshes were just about their body width.

Tumbler beetles, like a number of other water beetle families, are dependent on atmospheric air. Since their wing covers are trimmed at the end and the finely hairy tip of the abdomen is exposed, you can see the air hanging there as shiny metallic vesicles. Their specific weight is reduced by the air carried along by the surface of the water under the wing covers, so that they have to cling to underwater.

They have glands from which they can release toxic and paralyzing substances that cloud the water. The secretion is distributed outside of the water with the hind legs on the dry body surface.

Copulation occurs on or under the water, in some species on land. The eggs are attached to aquatic plants in strings under water. After ten days to three weeks, the centipede-like larvae hatch and then stay in the sludge layer of the bottom of the water and search for prey there. Your mandible partially traverses a channel through which digestive juices enter the packed victim ( extraintestinal digestion ). The larvae breathe the oxygen dissolved in the water with the help of tracheal gills .

To pupate, the larvae rise out of the water and, as is typical for the species, transform themselves either on aquatic plants or in small burrows or in a cocoon made from body excretions, plant parts and soil . After about one to nine weeks, the young beetles hatch and overwinter on land under stones, on parts of aquatic plants above the water and probably also under water. In this case, the vital oxygen is presumably obtained from gas bubbles that are found on aquatic plants.

Systematics

Around 800 species have been described worldwide, of which around 13 live in Central Europe , while 19 species and subspecies are known in Europe .

The following list gives an overview of the species native to Europe.

Family Gyrinidae

credentials

  1. ↑ Gyrinidae. Fauna Europaea, Version 1.3, April 19, 2007 , accessed on July 26, 2007 .

literature

Web links

Commons : Gyrinidae  - Collection of images, videos, and audio files