Insect flight

The insect flight is the oldest way of moving through the air and is comprised of various flying techniques. There is no fundamental difference to the flapping flight of birds regarding the crucial for flying forces of lift and drag: The on - and deduction- wings also serve as wings and drive as their leading edges are reinforced, while the rest remains elastic. Due to the smaller average size of flying insects, however, the impact frequency of their wings compared to the vertebrates is much higher.

The wings of insects wings are made ​​of chitin, which have arisen evolutionarily from protrusions of the skin. The flying insects are the most diverse group in the entire animal kingdom and most species have two pairs of wings. However, the Vierflügeligkeit hinders the fly, so there is an evolutionary tendency to Zweiflügeligkeit.

Flying at low and medium Reynolds numbers

Depending on the size of the insect and its airspeed, the air for the insect is different " tough ". Especially small insects therefore "float" in the air so tough because of their size and flight speed for them is like water (cf. Reynolds number, see also Web Links: " When the air is sticky "). They have therefore no flow- wing, but only brush -type resistance generator such as the bristles or thrips.

Larger or faster flying insects usually use transparent membranous wings. Thereof can either be reduced to the rear pair of so-called " halteres " which merely rotate the mass balance to be used as the wings and centrifugal tool ( in the Diptera, such as mosquitoes and flies).

When flying the wing downstroke of the top rear is carried forward and downward with horizontal wing position. Thus, the air resistance in the vertical direction at a maximum and in the horizontal direction is minimal. Thus, a high lift and a minimum rear engine is generated. In the upstroke of the wings from the front bottom is moved rearward above in the vertical wing position. This results in a minimum air resistance in the vertical direction, and a correspondingly low output, and a maximum resistance in the horizontal direction and corresponding to a maximum acceleration. This division of the antagonistic muscle groups in construction and tunneling has an approximate equilibrium of forces result which is for the mutual contraction triggering of the antagonists in the indirect flight muscles by stretching of considerable importance.

From the front pair of wings and a horny wing covers can be formed, which generates a fixed-wing lift in flight, while the larger, membranous rear wings pair is responsible for the excavation ( eg Coleoptera, beetles).

But there are also numerous species in which both pairs of wings are fully developed. The dragonfly wings of dragonflies ( Anisoptera ) is seen as a masterpiece of nature. At each of the four wings of a nascent by embedded eddy current rolling low drag laminar airfoil (ie an airfoil with high thickness reserve) was formed by means of the shape of the trachea and membranes in the air stream, which can be used for gliding, steady flapping flight and high-speed flight. Trim tanks are incorporated in the wings ( Pteristigmata ) allow an additional control. Although the wing makes up only 2 percent of the total weight of the dragonfly, it enables unmatched stability and excellent flight characteristics, where it accounts for more than 50 percent of the surface of the animal. This ratio of wing weight and surface fraction to total weight is unmatched across the human aviation.

Smaller insects use to boost recovery in flapping flight usually the technique of leading edge vortex. Due to the up-and their sharp wing leading edge, a vortex is generated along this edge, which can be used directly for the lift, where the rear part of the resulting vortex roll off the tee the wings sucked upwards upon impact the wing pushes up. This explains the outstanding flying characteristics of butterflies ( Lepidoptera), some of which may undergo several intercontinental flights of up to 4,000 km in the flapping flight in their lives, such as the monarch butterfly.

Flight muscles

The movement of the wings is done with either the indirect or the direct flight muscles. Direct " drive " is regarded as the original one.

As a wing-beat frequencies for different values ​​of 0 insects ( dragonfly in gliding ) up to 1046 Hz with midges ( genus Forcipomyia, Ceratopogonidae ) were measured. However, since it is impossible that a muscle is activated in this frequency by direct nerve impulses, as the latency and absolute refractory period of the action potential of a nerve limits the maximum frequency at about 800 to 1000 Hz, contraction in insects with indirect flight muscles, the muscles themselves constantly at overstretch. Since very small insects can generate the necessary for the flight air forces only with correspondingly high wing beat frequencies, they always have an indirect flight muscles. The airworthy representative of the primitive, direct type all have a certain minimum size ( grasshoppers, dragonflies).

Indirect flight muscles

The name comes from the fact that the muscles are not directly linked to on the wings, but the muscle power is transmitted indirectly via the skeletal elements of the thorax on the wings. The authorities responsible for the wing downstroke muscles are arranged along the thorax ( Longitudinalmuskeln ), responsible for the upstroke muscles pull the " back " of the thorax to its "belly" ( Dorsoventralmuskeln ). The deformations of the thoracic skeleton transmit the muscle force on the wing.

During flight, is observed in a reasonably regular intervals, action potentials of motor neurons, leading to the flight muscles in the release of calcium ions from the sarcoplasmic reticulum. However, the calcium concentration in the cytoplasm of muscle cells ( Myoplasma ) is not the cause of the contractions in this particular muscle type. Triggers the contraction of a muscle cell by its strain, which occurs in flight by their antagonists. The presence of a certain myoplasmatischen calcium concentration is a necessary but not sufficient condition for the contraction of the indirect flight muscles. Perhaps, however, the first muscle contraction by an initial calcium secretion triggered when the stationary system, caused by an action potential of a motoneuron.

The system is Stopped by the absence of action potentials of motoneurons, since then the calcium concentration in the Myoplasma by ion reabsorption decreases so much that contractions can no longer take place.

The contractions of the muscle cells have been different than usual muscle cells, because the myosin heads bend over by a conformational change though, but do not detach from the actin to make a fresh set on another Aktinabschnitt ( "biological gear " of the muscles ). Therefore, the shortening of the flight muscle is extremely low and must be transmitted through a mechanical translation on the wing. This translation is achieved inter alia through a chain of one-armed levers by which power is transmitted from the front part of the thorax back, the Scutum, the rear back ( scutellum ) in order from there over the ansitz border on both sides of the scutellum Tergalhebel forward again brought to the wing joints to become.

Already because of this mechanism, in which both wings can only be simultaneously or cut off, the fly does not have the option of jacking forces on both sides must be different when flying, to be produced by a different beat frequency. Instead, they can modify the amplitude of the wing beat, as well as the angle of attack of the wing on both sides separately. This is achieved through a highly complex wing-joint construction and a series of thin parking muscles, which can adjust the joint each match.

The wing-beat frequency of insects with indirect flight muscles is determined by the air and inertia forces that oppose muscle contraction. The flight muscles not to contract either in full due to the strain- induced contraction, or. For changes of wing beat amplitude or wing position, which are used for flight control, but changes the drag on the wing, which opposes the force of contraction. This then changes the wing beat frequency of the insect. In the experiment, one can wax observe the dependence of the beat frequency of the mechanical properties of the entire system can be regarded as a resonance system to fly thorax fixed by shortening or by weighting the wing.

The control of the flight muscles can be extremely primitive, and be linked to the message of ground contact of the tarsi of the legs insects (such as in the fly ). To start the Fly just jumping off the ground, all legs not report contact with the ground and the flight muscle is then started.

When landing an answer or several legs contact with the ground and the wing muscles are stopped. Attached is a fly on her chest without her legs have contact with the ground, their wings often suggest a very long time.

The indirect flight muscles of flies and other insects is one of the tissues that hold the highest energy expenditure. Electron micrographs show an extreme density of mitochondria, which serve all cells as " powerhouses ". Due to the enormous waste heat production during flight an efficient cooling system is needed. Bees and probably fly use here - as well as mammals - the very efficient evaporative cooling. The insects pump the air heated by the flight muscles in the thorax hemolymph in the head and gagging from a drop of liquid exiting the trunk and then evaporates. In flies that are attached to the thorax top, one can observe very nice these drops after some time. The slope of the insects to fly, going at high humidity sharply.

Direct flight muscles

In primitive insects such as dragonflies and mayflies, one finds a direct drive. The wings are here connected directly to the antagonistic muscles. The control of the movement is analogous in the direct approach to the wings to control the skeletal muscles in vertebrates (eg, flexors / extensors in the arm muscles ). The contractions are thereby directly triggered by the nervous system on action potentials of motoneurons. As with running movements are in the central nervous system of such insects certain nerve Enver circuits, which are also called pattern generators and produce the contraction behavior of the flight muscles as an action potential sequences.

Air combat techniques

Recent studies of dragonflies in flight have shown that dragonflies are able to maintain their position relative to the head and the compound eye of the insect, which they want to attack, constant. Thus, the position of the approaching bubble in the eye of her victim remains constant, the attacking dragonfly is not perceived. Dragonflies males also struggle with the reinforced wing leading edges with each other in order to have better reproductive opportunities by selling competitors.