Female octopuses throw debris at annoying males, researchers find

TORONTO -- Female octopuses have been observed "throwing" objects at males who harass them, including during unwanted mating attempts, according to new research.

The study, which was published on the pre-print server bioRxiv and has yet to be peer-reviewed, captured female octopuses on camera using their tentacles to gather debris, including shells, silt and algae, and launch it toward other octopuses with a jet of water.

"Some throws appear to be targeted on other individuals and play a social role, as suggested by several kinds of evidence," the researchers wrote. "Some throws were directed differently from beneath the arms and such throws were significantly more likely to hit other octopuses."

Researchers have studied this peculiar behaviour in octopuses off the eastern coast of Australia since 2015. While it's common for octopuses to perform similar throws when building and maintaining dens, the act of throwing is rarely seen by any creature in the wild, much less in a social context.

"Throws targeted at other individuals in the same population, as these appear to be, are the least common form of non-human throwing," the researchers wrote.

Of the 101 throws categorized during the study, 36 were deemed to be performed in a social context, while more than half were at least partially social.

Social throws were defined as those that occurred within two minutes of an interaction with another octopus. Interactions included fights, mating attempts and approaches or reaches followed by an apparent reaction.

"Throwing in general is more often seen by females, and we have seen only one hit (a marginal one) from a throw by a male," the researchers wrote. "Octopuses who were hit included other females in nearby dens, and males who have been attempting mating with a female thrower."

Of the 24 octopuses observed throwing debris, 11 did so in a social context. Among octopuses that were hit by a throw, none fired back, nor did any hits initiate a fight.

In December 2016, one female threw debris 10 times at a nearby male who had repeatedly tried to mate with her, hitting him five times. These actions, combined with the male's apparent efforts to dodge the thrown objects, may indicate intent.

"In one hit, the female's preparatory motions included a turn towards the male, and material was emitted between arms R1/R2, bringing the male directly into the path of the throw," the researchers wrote. "This sequence is also notable for the behaviors of the male who was the apparent target of the hits."