It’s no wonder that, with so many arms, octopuses turn out to be great throwers. They can even target other octopuses with bits of seafloor debris – and score a direct hit.
For the first time, researchers have observed the famous brain cephalopods deliberately throwing clumps of sand, bits of seaweed, and even seashells at each other, though they don’t actually throw themselves with their arms like people do. Instead, they use their arms to pick up projectiles and then propel them using jets of water expelled from a siphon placed under their arms. Scientists have captured video footage of this unusual behavior in dusky octopuses (octopus tetricus) at Jervis Bay on the south coast of New South Wales in Australia and described their findings Nov. 9 in the journal PLOS One (opens in a new tab).
“In some cases, the thrown material hits another octopus or another object (a fish or a camera),” the scientists wrote in the study.
After reviewing 24 hours of footage recorded on stationary underwater cameras in 2015 and 2016, the study authors identified 102 examples of about 10 octopuses picking up objects and throwing them. Often the objects would fly up to several lengths from the thrower’s body.
“Doing this underwater, even for a short distance, seems particularly unusual and quite difficult to do, which makes it an even more striking behavior,” co-author of the study. David Schel (opens in a new tab)professor of marine biology at Alaska Pacific University in Anchorage, Live Science told Live Science in an email.
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Both male and female octopuses threw debris, although two females made about 66% of all throws. As for what motivated the octopuses to start throwing debris, about 32% happened while the octopuses were cleaning up their dens. But 53% of slime releases happened when interacting with another octopus, a fish, or one of the cameras.
Other octopuses were scratched by the lobed debris in 17 cases. In some incidents, the target would raise an arm just before a missile was launched, “perhaps in recognition of the act in preparation”, the scientists wrote. “Octopuses in the line of fire ducked, raised their arms in the direction of the thrower, or paused, stopped, or redirected their movements.”
But were the launchers intentionally trying to hit their octopus targets?
“Throws during interactions differed from throws when other octopuses weren’t present,” Scheel said. “Throws that hit an apparent target were a little different, in a way reminiscent of aiming, from throws that didn’t hit,” implying that the debris jet was targeted.
Humans usually teach toddlers that throwing things isn’t the best way to communicate. But for other animals that live in close-knit communities — like chimpanzees, capuchin monkeys and dolphins — throwing objects at members of the same population can be an important social signal, the study found.
Octopuses are known to be extremely skilled and able to manipulate various objects. For example, the veined octopus (Amphioctopus marginatus) stacks and transports coconut shells, which he uses to build a “mobile home”. But octopuses, as a rule, are not social creatures; they usually live alone and when they encounter other octopuses they sometimes fight them or even eat them.
However, in recent decades, a growing body of evidence suggests that octopus interactions in some species are more complex than previously thought – and throwing objects may be a way the animals communicate, the scientists report. .
In the areas of Jervis Bay where dusky octopuses live, food and shelter materials are plentiful; outside of these patches of suitable habitat, resources are scarce. This could explain the unusual density of octopus populations there, which, in turn, would increase the number of encounters between creatures that would likely prefer to be the only octopus in town. Therefore, throwing debris may be a way for these normally solitary creatures to manage interactions with their octopus neighbors — including unwanted sexual advances, the researchers wrote.
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