A crab sinks to the bottom in a tank of water and tries to crawl away. She doesn’t get far. An octopus crouching in a tube rushes in, pulls itself over the crustacean, and retreats with the prey (the scene can be seen from around minute 0:46 of the video). What at first sight seems like the hasty attack of a greedy robber follows an effective system. Scientists from the University of Minnesota have observed octopuses in captivity while hunting and have discovered fascinating things about the eight-legged friends.
For a study that they published in the journal “Current Biology”, the researchers examined, among other things, whether octopuses prefer certain arms when hunting and use them differently, i.e. whether they are “left-handed or right-handed” (of course, taking into account that the animals each have four tentacles on the left and right).
For the study, the scientists observed the Californian two-spotted octopus. The animals grow to about the size of a tennis ball and live for about two years. The researchers numbered the arms on either side of the body and dropped different prey items into the octopus’ tank: crabs and shrimp. The cephalopods lurked in their hiding place, one eye forward. The hunting scenes were filmed and evaluated.
The prey animals were chosen because they each require a different hunting tactic, they say. Crabs move more slowly, while shrimp can swim away quickly with a flick of their tail. Here’s what the researchers observed: When chasing crabs, the octopuses pounced on the prey with a swift, feline motion. If there was a shrimp in the tank, the robbers proceeded more slowly, more deliberately, so as not to frighten their prey and possibly let it escape. The octopus first slowly groped its way forward with an attacking arm. Only after that arm had grabbed the shrimp were the nearest neighboring arms deployed to provide support.
No matter what prey was in the tank, each octopus would always attack second arm first. Whether with the second from the left or right again depended on which side the eye was on whose field of vision the object of desire was moving.
Flavie Bidel, lead author of the study, was particularly surprised at how predictable the hunting movements of all the animals observed in the experiment were. Above all, the fact that the attack was always carried out first with the second arm is remarkable given that the movements initially appear so unpredictable. The findings of the study should be useful in future in the development of robots and underwater vehicles.
Those: University of Minnesota
