Tentacle Tactics

How does an Octopus hunt?

It's a sort of call to arms.

In its small glass aquarium, an octopus is coiled placidly on its den. Then a crab falls into the tank.

The octopus flings itself over the crab, engulfing its prey in a cloud of arms and legs. 

However, there's order to this chaos of limbs, according to a new study. Scientists who observed how the octopus hunts found that the creature almost always uses its second arm from the center to grab for prey, and when it needs backup, it turns to the arms closest to that second appendage.

Reviewing hundreds of videos of octopus-on-prey action, Trevor Wardill, a professor of ecology at the University of Minnesota who is an author of the new paper, and Flavie Badel, a postdoctoral researcher in Dr. Wardill's laboratory, identified a number of moves.

Octopus limbs ''are highly flexible to some really amazing level,'' Dr. Wardill said, capable of taking on nearly infinite arrangements and forms to a degree that may appear random.

But each limb might have a role, the study suggests. All the swirling might obscure a carefully choreographed response.

To understand what's going on within the brain and limbs of the octopus, the team would like to be able to record what happens in the animal's nervous system as it leaps into action.

For Dr. Wardill, Dr. Bidel and their colleagues, the answers lie ahead, on the other side of experiments where myriad octopuses dance in a rain of snacks. [Veronique Greenwood]


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