Angry octopuses caught hurling silt, shells and algae at one another


Octopuses have been observed throwing around debris, sometimes at one another and especially when they show visible signs of anger.

A team of researchers based at the University of Sydney recorded the behaviour of a group of 10 common Sydney octopuses in Jervis Bay, New South Wales, Australia over several days in 2015 and 2016 using underwater cameras.

The octopuses were seen gathering up material such as silt, shells and algae and propelling it using a jet of water squirted from their siphon. In this manner they were able to fire material several body lengths away.

The researchers spotted 102 instances of the behaviour across 24 hours of footage spread throughout the observation period.

Around half of the throws occurred during interactions with other octopuses, such as arm probes or mating attempts and around 17 per cent of the objects thrown hit other octopuses.

This suggests that the octopuses are capable of targeted throws towards other individuals – a behaviour that has only been previously observed in a few non-human animals, the researchers say.

Although it is unclear exactly why the octopuses are throwing the material around, the researchers noticed that the animals that changed their skin to darker colours – a behaviour usually interpreted as a display of aggression – did so more often.

“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,” said lead researcher Professor Peter Godfrey-Smith, of the University of Sydney.

“Octopuses that displayed uniform colour, dark or medium, threw significantly more often with high vigour, while those displaying a ‘pale and dark eyes’ pattern threw more often with low vigour.

“Throws by octopuses displaying uniform body patterns, especially uniform dark patterns, hit other octopuses significantly more often than in other body patterns.”

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