A new article from New Scientist reveals a fun twist to an earlier study of octopus behaviors:
In 2015, Peter Godfrey-Smith at the University of Sydney and his colleagues filmed several common Sydney octopuses (Octopus tetricus) interacting at a site in Jervis Bay dubbed "Octopolis". It is one of the few places in the otherwise sandy sea bottom where octopuses can make dens, so there are an unusual number of the animals in a small area.
The cameras captured fights, matings and an extraordinary behaviour that the team calls throwing. "It's hard to know how best to describe it," says Godfrey-Smith.
The way these octopuses launched these objects was kind of fun — essentially holding them under their bodies with their tentacles, then blasting the objects with streams of water to launch them projectile-style across the city (or at least over a few body lengths' worth of distance).
At first, the scientists believed that the octopuses were using this practice to discard of leftover meal parts or clear out new dens for themselves. But after further observation, the researchers reached another conclusion: they're deliberately shooting the objects at other octopi. As described in the paper:
Some throws appear to be targeted on other individuals and play a social role, as suggested by several kinds of evidence. Such throws were significantly more vigorous and more often used silt, rather than shells or algae, and high vigor throws were significantly more often accompanied by uniform or dark body patterns. Some throws were directed differently from beneath the arms and such throws were significantly more likely to hit other octopuses.
What's more, a significant majority of the throws came from only two female octopuses
Out of 102 throws in the 2015 data, two reliably reidentified females were responsible for 67 throws (41 by octopus T23F and 26 by T1F). For both T23F singly and both together, this was significantly more than expected under a binomial distribution, assuming four or more potential throwers (p=<0.001). These two individuals were responsible for at least 66% of all throws, and likely another 5 throws when identifying marks were not visible on video to confirm a suspected ID. The most active male mentioned above may have been the next most frequent thrower, with 5 throws in total, though he could often only be provisionally reidentified until he was bitten by a fish midway through the recording period, leaving a visible scar.
There were 90 throws by females and eleven by males, a ratio of 8.9:1. … Over half of all throws (53%) occurred in a context that was at least partly social (36 throws in social contexts (36%); 17 in mixed contexts combining social and den-cleaning (17%); 32 during den-cleaning (32%); 8 after eating (8%); and 8 with no apparent context (8%)).
So why do the scientists think it's about harassment? Here's what they observed:
Octopuses who were hit included other females in nearby dens, and males who have been attempting mating with a female thrower. In one period of interaction, a throw that was a hit was followed by a couple of events where the thrower pushed shells into the den of the same neighboring octopus, without throwing them.
A large number of throws were also made by octopuses while at a particular den, where octopuses may have experienced heightened arousal for several reasons. This den, flanked by several others, was the position on the site at which the most social interaction occurred. The most active male visited all the surrounding likely females at various times, and also spent time sitting in the open near this den. This den was also near a camera, and was the den from which most of the camera-directed throws occurred.
So maybe it's not about men in general, and maybe it's just this one octo-dude who really pissed them off.
Also, one of the octopuses apparently hit a fish with a flung shell, though the researchers believe it was accidental.
Female octopuses throw things at males that are harassing them [Michael Le Page / New Scientist]
In the Line of Fire: Debris Throwing by Wild Octopuses [Peter Godfrey-Smith, David Scheel, Stephanie Chancellor, Stefan Linquist, Matthew Lawrence / bioRxiv]