Wild octopuses have been observed underwater throwing silt, shells and algae at each other.

While studying the unique physiological trait, researchers from the University of Sydney, Australia, found that both sexes throw but females do it more often. In one instance, a female octopus repeatedly launched silt at a male that had been trying to mate with her, with the male frequently ducking to avoid the hits.

Octopuses also threw the remains of their meals and materials to clean their dens. There was even a case where they hurled silt towards one of the researchers’ cameras, and another two cases where throws hit fish.

The study was led by science professor Peter Godfrey-Smith, who said: “In some cases, the target octopus raised an arm up between itself and the thrower just before the throw, perhaps in recognition of the imminent act.”

But are they really throwing? Yes, said Professor Godfrey-Smith, but not in a human sense. Octopuses throw by gathering material in their arms, holding it in their arm web and propelling it using their siphon – a funnel next to their head – sometimes several body-lengths away.

He and colleagues undertook the research using stationary GoPro cameras to film up to 10 common Sydney octopuses for over 20 hours at a marine reserve in Jervis Bay, New South Wales, Australia, and later analysed the footage.

In instances where the throwing might be interpreted as aggressive, Godfrey-Smith said this could be due to cramped conditions. Octopuses inhabit the site in Jervis Bay in unusually high densities.

“Most throws do not hit others,” said Godfrey-Smith.

“Only a minority of cases appear to be targeted. I’d speculate that a lot of the targeted throws are more like an attempt to establish some personal space but this is a speculation, it’s very hard to know what their goals might be.”

The research was published in the journal PLOS ONE.