Also in a swarm a desert sprinkhane is an independent individual

It is a well -known phenomenon at desert sprinkowns: if they are with too much, they will swarm. Soon a ruthless, crop destructive plague can occur. For a long time it was assumed that such a swarm adheres to physical laws: at high densities, the locusts would no longer behave as unorganized particles in a gas, but as organized particles in a liquid.

But German biologists and physicists Write now in Science That that assumption is incorrect. Based on field research and Virtual Reality-They conclude that the individual locusts do indeed make decisions instead of behaving like passive particles.

The desert sprinkhane (Schistocerca Gregaria) occurs in an area from Mauritania to India. In principle, the insects live solitary; They only look for peers to reproduce. If there is a lot of precipitation and there is enough green vegetation, the number of locusts soon increases with a factor of 10 to 20. And with such rapidly increasing numbers something crazy happens: changes suddenly occur in behavior and appearance. The locusts become group animals, less picky in their food preferences. Their hormone balance is also changing. They discolour from light brown or light green to bright yellow. The solitary locusts have become 'Gregair', group -forming – ready to swarm.

Typical behavior of Self-propellelled Partleswas the thought for years. In groups, organisms (whether it is bacteria, grasshopper, sheep, birds or people) would move collectively according to physical models, of which the VICSEK model (designed in 1995 by the Hungarian Tamás Vicsek) is one of the more famous.

Previous experiments with young Gregaire desert sprinkhans seemed to confirm those theories. For example, a lab showed that enlarging the sprinkhan density on a circular surface leads to a transition from unorganized to organized movement, as with a phase transition from gas to liquid. Yet that assumption is incorrect, the current researchers register Science. Individual grasshoppers in a swarm do not adapt to their neighbors indiscriminately. Their behavior corresponds much better to cognitive models about decision -making than with the physical models.

Cut antennas

To investigate how Gregaire grasshoppers tailor their movements to those of their swarm mates, the German scientists first did field research. During a large desert sprinktheop pest in Eastern Africa, at the beginning of 2020, they cut off the antennas (to prevent smell) and covered the eyes with a layer of paint (to prevent polarized view and 'just' vision). The poor insects were then put back with the rest, to see to what extent they marched with the rest of the group.

Only the completely blinded individuals could no longer come along. In contrast to smell, so crucial, the researchers concluded for swarm behavior. That led to the next step: creating a VR model, in which real desertsprinkhanes can join a swarm of virtual relatives. This showed that the extent to which they adapt to the group is not so much related to the density of the swarm as with the quality of the stimuli offered. In other words: the more convincing the neighbors move in one line, the stronger an individual grasshopper is inclined to move along. Sprinkhaans 'choose' themselves to swarm, according to the researchers.