Why do octopuses throw projectiles at fellow octopuses?

Octopuses are not known to be particularly social. They hunt alone and fight regularly when they meet and cases of cannibalism have been noted. In 2012, Peter Godfrey Smith, then a researcher at New York University, and Australian diver Matthew Lawrence noticed dark octopuses. (octopus tetricus) They live in a group on a rock formation in Jervis Bay, south of Sydney, Australia. These octopuses occupy a group of dens surrounded by empty shells that the researchers dubbed the Octopolis. Since then, a second site of the same species has been located hundreds of meters from the first site, Ocantis.

The researcher, now at the University of Sydney, and his team recently photographed two groups of dark octopuses and observed a social behavior rare in land animals: These octopuses have an alarming tendency to hurl projectiles at their congeners.

Octopuses do not throw like humans javelin, by transferring energy to the projectile by arm movement. The technology they use is akin to the mechanism of an air rifle. They collect shell debris, silt, or algae in a pocket formed by the mantle, an extended membrane at the base of their eight arms. They then place the siphon (which they generally use to breathe and possibly propel themselves) in an unusual position, between their arms, to blow water into the sinus and build up pressure there. When the arms are opened, the contents of the pocket are displayed at a distance that can reach a few tens of centimeters.

In Jervis Bay, octopuses are a species Octopus Tetricus Use this technique in particular to keep leftover meals out of their den, as has already been observed in other species of octopuses in captivity. However, scientists have also noted that this type of throwing sometimes hits a nadir.

Is it accidental? Several specific behaviors, such as a color change associated with aggressiveness, preferential selection of silt as a shot, more aggressive throws, or even attempts to dribble when a shot is approaching, indicate not. Scientists believe they have enough evidence to conclude that the wrasses are deliberately directed towards congeners, although the social role of such behavior remains difficult to determine. For example, the team never observed an aggressive response from a target or a reaction.

This study includes octopuses in the shortlist of animals that use target projectiles, along with Archer fish, and in the shorter list of those who target their mates. This latter behavior has long been considered a typical human idiosyncrasy, but some other species such as chimpanzees or capuchin monkeys also seem capable of it.