The common Sydney octopus, Octopus Tetricus Nature Picture Library / Alamy
A look at footage of octopuses from Australia showing them throwing silt and shells suggests that they are targeting other octopuses. Most often, the throwing is done by females, and sometimes at males who are harassing them.
Peter Godfrey Smith, University of Sydney, and his associates filmed common Sydney octopuses (Octopus Tetricus) at an area in Jervis Bay called Octopolis. This is the only place in the sandy sea bottom that octopuses are able to make dens. There are a lot of them in this small area.
The team called throwing the action captured by the cameras. Godfrey Smith says it is difficult to put into words.
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The octopuses keep silt, alga, or other objects under their bodies in tentacles. They then angle their siphons to shoot water at projectiles, propelling them to several lengths.
The throwing behavior was used to discard food or excavate dens. However, the videos showed many instances in which octopuses struck other people with thrown objects.
Godfrey Smith described the behavior in 2015, but he wasn't sure if they were deliberately targeting other octopuses. Or if they just hit them by accident.
The team now has more footage. A detailed analysis also showed differences in the throws targeted at others and those for clearing dens, suggesting that the octopuses may be deliberately targeting other animals.
For example, in 2016, a female octopus tossed silt at a nearby male who was trying to mate with her. He was hit five times. Godfrey Smith says that this sequence was one of her favorites.
The male attempted to duck on four occasions. However, he did not always succeed. In two instances, he was able to anticipate the movements of the females and start avoiding the silt before it was propelled at his face.
The octopuses were more likely than other species to target others with silt and more powerful throws when they were targeting them.
Moreover, throws during den-building were almost always made between the two front tentacles. The octopuses would sometimes throw at other animals by aiming the throw between their first and second tentacles. Godfrey Smith says that this suggests some kind of targeting.
One time, researchers saw an octopus hurl a shell at another octopus and then hit it with a tentacle, much like a frisbee.
Continue reading: Octopuses were once thought to be solitary, until they became a social species.
Although there are many wild animals that throw or propel objects at other animals, it is only a few, such as chimpanzees who have been known to target their species. It is very rare. Godfrey Smith says that throwing objects at other members in the same community is very rare.
Two times, an Octopus hit a fish on two occasions. However, one of these collisions seemed to be accidental. Sometimes, the animals seemed to be aiming at the camera and hitting the tripod twice.
Although the throwing may be used as an attack method, the team has not seen any targeted octopus react by throwing or attacking back. Furthermore, throws made after intense social interactions don't seem to be directed at another octopus, but rather into empty space. This suggests that the animals may be venting frustration.
One case was where a male tried to approach a female but was rejected. He then threw a shell at random and changed its colour.
After a paper suggesting that polar bears may use rocks or lumps ice as weapons in hunting, the team decided to publish their findings as a preprint.
Reference: bioRxiv, DOI: 10.1101/2021.08.18.456805
