Octopus tetricus debris throwing in the wild. Panel A - Octopus projects silt (from video by Peter Godfrey Smith); B an octopus is hit by a cloud silt through the water by a throwing octopus. (left; see SI to video of the event); C, D The mechanics and throwing behavior of Octopus tetricus, C shells and silt are held in the arms prior to the throw. C siphon is removed from the web and under the arm pair of the back. Rebecca Gelernter illustrated. Credit: biorxiv (2021). DOI: 10.1101/2021.08.18.456805
Researchers from Australia, Canada, and the U.S. discovered that female octopuses can sometimes throw silt at male octopuses when they are trying to mate. The research group has published a paper detailing their findings on the bioRxiv preprint site.
In 2015, researchers recorded instances where octopuses were throwing things at each other. It was unclear at the time if other octopuses had been deliberately targeted or if this was an accident. They returned to Jervis Bay off the coast of Australia to find out. This is where large numbers live.
Researchers were able to observe that female octopuses engage in multiple types object-throwing activities by making additional recordings and carefully studying them. Most of the time, throwing silt or shells was just a way to move material or build a nest. They saw less often what appeared to be attempts by females, to throw material at nearby males, usually one trying to mate.
Researchers discovered that hurling was accomplished by holding onto material like rocks, silt, or shells under the body. The material was then placed on top of a siphon, which the creature uses to quickly push out water. The material was then propelled ahead of the water jet, sometimes up to several body lengths.
Researchers found numerous instances in which females targeted males while reviewing the tape. One scenario showed that a female had thrown silt at a male 10 times. The males were more successful than the females in ducking objects thrown at their heads. The throws intended to remove material were done differently to those directed at another octopus. This involved tossing between two front tentacles. Suitor-repelling projectiles were typically launched between the first tentacle and the second tentacle. One female was also seen to throw a shell using one of her tentacles. They did not observe any evidence that males would retaliate by throwing things at females who were being targeted.
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More information: Peter Godfrey Smith et al., In the Line of Fire, Debris Throwing By Wild Octopuses. biorxiv (2021). Peter Godfrey Smith et al. In the Line of Fire, Debris Throwing By Wild Octopuses. (2021). DOI: 10.1101/2021.08.18.456805
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