How octopuses coordinate their eight arms

When hunting, octopuses adapt the use of their eight arms to their prey. Crabs, which are slow to flee, usually overwhelm the animals with the rather simultaneous use of several arms - sometimes they jump on the prey like a cat on a mouse.

On the other hand, they use their arms more selectively and one after the other when hunting quickly fleeing shrimp, as a team of US researchers reports in the journal Current Biology. The second arm on the right and left side of the body, viewed from the front, has a dominant function.

If you just look at an octopus for a moment, the movements usually don't seem repeatable, says study leader Trevor Wardill. "They fidget around and just look strange when they move about." To analyze the movement sequences more precisely, the researchers filmed Californian two-spotted octopuses (Octopus bimaculoides) in an aquarium.

They added either white leg shrimp or fiddler crabs and watched the octopuses subdue the prey from their hiding place. The scientists were able to distinguish three approach strategies used by the octopuses: the animals approached from ambush, pursued the prey or cautiously crept up to it.

As the analysis showed, shrimp were more likely to be attacked from ambush or after sneaking up on them, while crabs were more often pursued. Next, the researchers analyzed the actual attack and how the four pairs of arms - the researchers numbered the arms from one to four on the right and left side of the body - are used in the process.

The slower crabs were more often overpowered by the simultaneous use of two to six arms. The second arm in each case dominated. The faster shrimp were attacked more cautiously and more specifically - often with the second arm first. Once this made contact with the prey, the octopuses secured their catch with the two adjacent arms.

The scientists continue to report that the arms on the left and right side of the body are basically equal. The use is often related to the field of vision: If prey animals were perceived with the left eye, the arms on the left side of the body would be used in an attack.

The analysis further showed that the octopuses used only a small part of all theoretically possible arm combinations when hunting. So she seems to be using her arms very purposefully indeed. The brains of octopuses and other octopuses are amazingly powerful. They cope with so-called maze problems in experiments more efficiently than most mammals.

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