Octopuses throw shells and sand at each other, and scientists captured their fights on video
It’s no wonder that octopuses with so many arms turn out to be great pitchers. They can even attack other octopuses with bits of seafloor debris – and score a direct hit.
For the first time, researchers have discovered the famous, intelligent cephalopods deliberately throwing clumps of sand, bits of algae, and even shells at each other, though they don’t actually throw their arms like humans do. Instead, they use their arms to collect projectiles and then propel them with jets of water ejected from a siphon under their arms. Scientists captured video of this unusual behavior in gloomy octopuses (Octopus tetricus) in Jervis Bay on the southern coast of New South Wales in Australia and detailed their findings Nov. 9 in the journal PLOS One (opens in new tab).
“In some cases, the projected 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 and throwing things. Often the objects flew up to several body lengths away from the thrower.
“Doing this underwater, even for a short distance, seems particularly unusual and quite difficult to do, making this an even more striking behavior,” study co-author David Scheel (opens in new tab)a professor of marine biology at Alaska Pacific University in Anchorage, told Live Science in an email.
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Both male and female octopuses would throw debris, although two females performed about 66% of all throws. What motivated the octopuses to start slinging debris, about 32% occurred while the octopuses were cleaning their burrows. But 53% of the sludge discards happened while interacting with another octopus, a fish, or one of the cameras.
In 17 cases, other octopuses were pelted by the lobed debris. In some incidents, the target raised an arm just before launching a missile, “perhaps in recognition of the act in preparation,” the scientists wrote. “Octopuses dived into the line of fire, raised their arms toward the thrower, or paused, halted, or redirected their movements.”
But were the pitchers intentionally trying to hit their octopus targets?
“The tosses during interactions were different from tosses when other octopuses were not present,” Scheel said. “Throws that hit an apparent target were a little different, in ways that suggested aiming, from throws that didn’t hit,” suggesting debris throwing was the target.
People usually teach toddlers that throwing things is not the best way to communicate. But for other animals that live in close-knit communities — such as chimpanzees, capuchin monkeys and dolphins — throwing objects at members of the same population could serve as an important social signal, according to the study.
Octopuses are known to be extremely dexterous and capable of manipulating various objects. For example, the veined octopus (Amphioctopus marginatus) stacks and carries coconut shells, who uses it to build a “mobile home”. But octopuses, as a rule, are not social creatures; they usually live alone, and when they come across other octopuses, they sometimes fight or even eat them.
In recent decades, however, a growing body of evidence suggests that octopus interactions in some species are more complex than once thought — and throwing things may be one way the animals communicate, the scientists reported.
In the regions of Jervis Bay, which are home to gloomy octopuses, food and materials for shelter abound; outside these stretches 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 probably rather 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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