In 2015 and 2016, researchers observed and filmed instances in which gloomy octopuses (Octopus tetricus) in Jervis Bay, Australia threw debris around themselves and sometimes at other octopuses.

This was the first time such throwing behavior has been observed in octopuses.

What was going on? Were these intelligent creatures merely rough-housing or having a pillow fight?

Led by Peter Godfrey-Smith at the University of Sydney, the researchers analyzed 24 hours of footage and identified 102 instances of such behavior amongst a group of about 10 octopuses.

They observed the octopuses gathering up material to throw; these might be items or debris like silt, shells, algae, sometimes even remnants of their meal. The octopuses then used a jet of water from their siphon to shoot the items through the water, sometimes causing them to land several body lengths away.

Female octopuses were responsible for 66 percent of the throws. About 50 percent of throws took place when there was interaction with other octopuses, like arm probes or mating attempts. About 17 percent of the throws hit other octopuses.

“Most throws do not hit others,” said Professor Godfrey-Smith, adding that only a minority appeared to be targeted. 

According to the press release, the researchers also observed the octopuses throwing out the remains of their meals and materials to clean their dens. Once, silt was even thrown at one of the researchers' cameras. In two other instances, fish were hit by the debris.

It was also found that dark-coloured octopuses—with the dark coloration suggesting aggression—tended to throw more forcefully and they were more successful in hitting another octopus. If the intent was to ward off the other octopus, such throwing actions were successful, as the other octopus would alter their behavior by ducking or raising their tentacles in the thrower’s direction.

Although the reason for the throwing behavior has not yet been determined, it has been suggested that octopuses are able to targeted throws towards other individuals.

A paper on this subject was published in the PLOS ONE journal.