Female Octopuses Throw Debris at Unwanted Mates Who Pester Them, Study Shows

Researchers in Australia recently discovered that female octopuses throw debris with a strengthened force at targets when they feel harassed. The researchers observed these females throw silt, algae and shells at unwanted mates.

University of Sydney researchers have been studying these wild octopuses on New South Wales' south coast since 2015. The female octopuses were recorded by underwater cameras which showed them strategically gathering shells, algae and silt into their arms before expelling the debris through a siphon toward other octopuses.

"Some throws appear to be targeted on other individuals and play a social role, as suggested by several kinds of evidence," researchers wrote in the study. "Such throws were significantly more vigorous and more often used silt, rather than shells or algae...some throws were directed differently from beneath the arms and such throws were significantly more likely to hit other octopuses."

While this is common behavior for octopuses, scientists had not fully understood the societal role these throws take. The scientists noted that it is a common behavior for these wild octopuses to move materials by scooping and pushing, which proves that the "throwing" action seems to be deliberate.

The scientists gathered data in three different contexts in which the octopuses threw objects. The first context was discarding eaten food with the arms. The other two were den maintenance and social. Den maintenance included the "rearranging or excavation of materials from in or around the den," the study explained.

"We categorized as social any throw that occurred during or within a two-minute window of an interaction with another octopus," researchers wrote in the study. "As noted above, interactions included fights, mating attempts, and approaches or reaches followed by an apparent reaction by another octopus."

Female octopuses throw silt at unwanted mates
While it is common for octopuses to throw debris, researchers found that during social interactions octopuses sometimes target unwanted mates. Researchers found these females throw silt, algae and shells. sko/Getty Images

Out of 100 "throws," scientists found that 36 occurred in a social context and approximately 53 "occurred in a context that was partially social." The researchers also found that nearly 11 of the 24 octopuses they studied threw in social contexts. They also found that social throws occurred after mildly aggressive interactions between octopuses including instances of unwanted mating.

"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 study stated. "Octopuses who were hit included other females in nearby dens and males who have been attempting mating with a female thrower."

The video recorded by the researchers also showed a female octopus throwing 17 times in a period of 60 minutes. Nine of these throws actually hit other octopuses, and of the nine "Eight were hits on a nearby likely female and one was a hit on the most active male."

However, similar evidence collected in December 2016 showed a female octopus targeting a male octopus who had previously been trying to mate with her. "In one hit, the female's preparatory motions included a turn toward the male, and the material was emitted between arms R1/R2, bringing the male directly into the path of the throw," the study stated. "This sequence is also notable for the behaviors of the male who was the apparent target of the hits."

The researchers never witnessed a hit octopus "return fire" by throwing materials back at the thrower. However, these octopuses seemed to anticipate the throws by ducking or moving out of the material's path. They also witnessed octopuses raising their arms in anticipation of the debris.

While there is numerous evidence that octopuses and other animals throw materials, it is rare that these "throws" are targeted at individuals and play a societal role."Octopuses can thus definitely be added to the shortlist of animals who regularly throw or propel objects, and provisionally added to the shorter list of those who direct their throws on other animals," researchers wrote in the study. "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."