Photography: Robert Cianflone/Getty Images
They hunt alone, are prone to fighting and even cannibalize each other. And octopuses seem to have another anti-social arm in their behavior: they launch jet-propelled clouds of silt, algae, and even seashells.
Researchers are studying octopus tetricusthe common Sydney octopus, filmed the cephalopods gathering debris in their front arms and web and propelling them away from their bodies using water ejected from their siphon – the latter having been moved between their hind arms at this effect.
While the team says these “squirts” appear to be used by octopuses to clean the den or to throw shells after eating, they also recorded the creatures hitting other octopuses with material in what appear to be shells. deliberate strikes.
Professor Peter Godfrey-Smith, first author of the research at the University of Sydney, said the behavior was surprising,
“The throwing – or propelling, or throwing – of gathered and held objects is rare in the animal kingdom. Propelling an object even a short distance underwater is particularly unusual, and also quite difficult to do,” he said.
Writing in the Plos One newspaper, Godfrey-Smith and colleagues report how, in 2015, they recorded more than 21 hours of video in Jervis Bay, off the south coast of New South Wales, Australia, at using fixed underwater cameras, capturing the behavior of about 10 octopuses.
Both men and women have been recorded performing ‘throws’. However, the team reports that the majority were women, with two of them accounting for 66% of the throws.
Of 102 throws, the team reports that 32% were related to octopuses cleaning their dens, while 8% occurred after eating, with shells making up the majority of material thrown by creatures in these settings.
However, 53% of recorded throws occurred within two minutes of one octopus interacting with another, whether fighting, mating or grappling.
These interactions also occurred in addition to another action, such as cleaning the den, and tended to involve silt as the primary material. Additionally, the researchers note that 33% (17) of those throws involved the material hitting another octopus.
It seems that such strikes could be deliberate. Among the evidence for this, the team found that octopuses using an unusual combination of legs to hold material, those that threw with great vigor and those that were darker in color when thrown were all more likely to strike. another octopus.
“Previous work on this site has shown that darker colors are associated with more aggressive behaviors,” the team writes.
While these strikes were typically jet propelled, in one unusual case the team reports that “a shell was, at least in part, launched by straightening one arm and hitting another octopus.”
The team adds that recordings from 2015, along with other footage, show examples of cephalopods making multiple throws over a period of time, often hitting other octopuses in the process. On some occasions, those in the line of fire appeared to raise an arm before the shot in preparation – or duck, during or just before the throw.
The team says it’s still unclear why the octopuses would target others, adding that footage did not show such behavior starting a fight, or resulting in “backfire”, while in some cases, throws were made into an empty space. Indeed, they write, it’s possible that octopuses simply hit each other as a result of interaction during other actions like cleaning the den.
But Godfrey-Smith suggested the strikes might have a purpose. “I think a lot of it feels like an affirmation of ‘personal space,'” he said. “In many cases, females threw material at male octopuses that attempted to mate with them… But in other cases, females threw and hit other females.”