In its small glass aquarium, an octopus is coiled placidly in its den.
Then, a crab falls into the tank.
The octopus scrambles to fling itself over the crab, wanting much less like a finely honed killing machine than a toddler who’s noticed a cookie, engulfing its clawed prey in a cloud of suckered legs and arms.
Nonetheless, there’s order to this chaos of limbs, in accordance with a paper printed Tuesday within the journal Present Biology. Scientists who noticed how the octopus hunts discovered that the creature virtually all the time use its second arm from the middle to make a seize for prey, and when it wants backup, it’s the arms closest to that second appendage that they create into play. The researchers additionally discovered that completely different prey are hunted with completely different techniques: Crabs get a transfer the scientists name “parachuting,” whereas shrimp, that are extra skittish and delicate to massive actions, are snared with a stealthy limb.
Octopuses appear to hunt extra by really feel than by sight. They’re typically discovered prospecting for crabs and different prey relatively than chasing them.
“They wander across the reef and so they speculate by sticking their arms down holes,” mentioned Trevor Wardill, a professor of ecology on the College of Minnesota who research the imaginative and prescient of octopuses and different cephalopods and is an writer of the brand new paper.
However generally octopuses will see a tasty critter dashing by and make a seize for it. Dr. Wardill and Flavie Bidel, a postdoctoral researcher in his laboratory, had been curious how this less-studied type of looking labored, so that they arrange high-speed cameras round aquariums with octopuses and dropped reside crabs and shrimp down a chute to see what the cephalopods did.
Reviewing a whole lot of movies of octopus-on-prey motion, they recognized a variety of strikes used time and again. There’s parachuting, as an illustration, the place the octopus pounces, spreads the webbing between its limbs to include the prey and makes use of its limbs to carry dinner into its mouth. There’s the snap-trap, the place two teams of arms prolong like a pincer across the prey.
There was additionally an odd little maneuver that the octopuses deployed after they had been confronted with a shrimp, which the scientists known as “waving.”
If a shrimp senses motion within the water close by, it’s going to flick its tail and zoom away, in what Dr. Wardill calls a “ballistic, get-the-heck-out-of-here” transfer. Within the movies, octopuses typically snaked an arm out in entrance of them, waving it gently, earlier than wrapping it tightly round a shrimp’s antennae and entering into for the kill. He speculates that this wavelike motion might be a means of spoofing the shrimp’s sensors: To the shrimp, it’d really feel about the identical as a bit of seaweed undulating close by, thus concealing the octopus’s actions.
The researchers had been additionally to see that octopuses tended to make use of the second arm out from the midline of their physique, on the facet dealing with the prey, to guide an assault.
“There should be a hierarchy within the mind of the octopus,” a strategy to management the order through which limbs transfer, Dr. Wardill mentioned.
Octopus limbs “are extremely versatile to some actually wonderful stage,” he added, able to taking up almost infinite preparations and varieties to a level which will seem random.
However every limb might need a selected position throughout a bout of looking by sight, the examine suggests. All that swirling would possibly obscure, to the common viewer and not using a high-speed digicam, a fastidiously choreographed response.
To know what’s happening inside the mind and limbs of the octopus, the group would love to have the ability to file what occurs within the animal’s nervous system because it leaps into motion. Does the mind recruit arms in particular groupings or in a sure order? Does the octopus react in another way in dim mild?
For Dr. Wardill, Dr. Bidel and their colleagues, the solutions lie forward, on the opposite facet of experiments the place myriad octopuses dance in a rain of snacks.