Typically solitary creatures, octopuses aren't exactly neighborly when fellow cephalopods encroach on their personal space, even if it means turning just about anything in reach into a weapon.

In a recently published study by a team of researchers in Australia, the US, and Canada, observations of wild octopuses casting shells and sand directly at other members of their species have raised questions over whether this unusual behavior is a deliberately antisocial act – or if passers by are accidentally in the line of fire.

Scientists first observed octopuses flinging objects at each other in a scene of seemingly heated argy-bargy in 2015 off the eastern coast of Australia, where such large numbers of Sydney octopuses (Octopus tetricus) congregate that scientists have dubbed the region Octopolis.

Octopuses Throwing
Debris throwing by octopuses in the wild. (Godfrey-Smith et al., PLOS One, 2022)

Now in a newly published study, they have determined that the flingers are mostly female – and they're probably, at least in some instances, trying to ward off overly amorous males.

"The throwing of material by wild octopuses occurs frequently at our two study sites. These throws are achieved by gathering material and holding it in the arms, then expelling it under pressure," the researchers write.

"There were 90 throws by females and eleven by males, a ratio of 8.9:1."

Many animals fling debris at others, and there are many reasons for doing so. It can be a threat or defensive behavior, or has to do with trapping prey. Most animals seen doing this, however, are flinging things at other species, not their own.

So, to determine why octopuses might like to throw shells, silt, and algae at each other, a team of researchers led by philosopher of science Peter Godfrey-Smith of the University of Sydney set out to observe the chucking in action.

Using non-invasive GoPro cameras left on-site, they recorded over 100 instances of the inhabitants of Octopolis flinging debris willy-nilly. The octopuses would hold material in their arms, and then use their siphons to blast a jet of water that would blow the material up to several body-lengths away.

As they analyzed their recordings, the researchers noticed that there seemed to be two main types of throwing. The first had to do with housekeeping, and keeping their cozy dens free of unwanted debris and food waste.

The second seemed a bit more targeted. Octopuses, determined to be (mostly) female, were observed throwing material at other octopuses in targeted attacks. Overall, shells were the most commonly thrown object, with 55 recorded instances.

For 33 percent of these targeted throws, the flung object actually hit the intended target, with silt being the best material for this task. The targets were either other nearby females, or males making attempts to mate.

In one notable instance, recorded in 2016, a female octopus threw material at a male 10 times over a period of 3 hours and 40 minutes, hitting it five times. Interestingly, octopuses that were hit with such ejecta made no attempt to retaliate, but did sometimes attempt to duck (although not always successfully).

Another, perhaps slightly more controversial explanation for this behavior could be that the throws are not always necessarily targeted, but could be a form of tantrum due to frustration.

After several dramatic interactions, the researchers observed that one octopus would throw things in a manner that didn't seem directed at the other octopus. Given how difficult it is to assign intent to animals, though, especially one as alien as octopuses, it is impossible to definitively conclude that this is the case.

Either way, it seems that the throwing does seem to play some sort of social role.

"Octopuses can thus definitely be added to the short list of animals who regularly throw or propel objects, and provisionally added to the shorter list of those who direct their throws on other animals," the researchers write.

"If they are indeed targeted, these throws are directed at individuals of the same population in social interactions – the least common form of nonhuman throwing."

This research was published in PLOS One.

An earlier version of this article was published in August 2021, when the study was at preprint stage.