This octopus was caught defending its space—by throwing things

For its distinctive way of defending its boundaries, consider Octopus tetricus, aka the gloomy octopus. If another creature gets too close, this octopus will respond by throwing things, according to a new study published recently in the journal PLOS ONE.

Native to subtropical seas off New Zealand and eastern Australia, these cephalopods recently were caught on camera throwing shells, silt, and algae at intruders who ventured too near their dens–the first time a throwing behavior has been reported among octopuses. The targets of O. tetricus–also called the common Sydney octopus–included various fish, underwater cameras, and even each other.

Though scientists aren’t totally sure what motivates the behavior, it may have something to do with “the octopus equivalent of personal space,” says Peter Godfrey-Smith, a professor at the University of Sydney in Australia and lead author of the study.

Aggression at close range

Godfrey-Smith and his colleagues collected dozens of hours of footage of gloomy octopuses near their dens in Australia’s Jervis Bay–and between 2015 and 2016, they observed more than 100 instances of the cephalopods chucking shells and silt. Because gloomy octopuses are abundant but space is limited space in Jervis Bay, the normally solitary animals are forced to live in close quarters, Godfrey-Smith says: “At this site, we see a lot of arm-pokes, probes, a bit of wrestling, and the like.”

About half of the hurling attacks Godfrey-Smith and his colleagues captured on camera appeared to be the result of one octopus invading another’s turf–and 17 percent of those attacks landed a hit on the invader. Godfrey Smith says that although it is difficult to determine an animal’s intentions, “I believe it is likely some of the hits were deliberate.”

In other instances, octopuses were seen using their throwing skills in order to throw food scraps and shells out of their dens. (Read why octopuses remind us so much of ourselves).

Jet-powered projectiles

To execute their throws, gloomy octopuses scoop up debris with their arms and shoot it toward their target with a powerful jet of water from their siphon, a tubular structure they use to pump water out of their bodies. Cephalopods can propel materials several feet away using this technique.

Octopuses can change the color of their skin at will to camouflage or communicate, with dark colors generally associated with aggression. Researchers found that individuals with darker skin tones were more likely to throw objects with greater force and to strike another octopus. They also observed that octopuses caught in a line of fire often reacted by avoiding or raising an arm in direction of the attacker.

The researchers found that the octopuses adjusted their throwing angle and force when throwing things at themselves. Silt was the most common artillery in octopus on octopus attacks.

Anti-social social club

While throwing things at one another may not help humans solve their problems, such behavior may “help manage social interactions where octopuses live in close proximity,” says Chelsea Bennice, a marine ecologist with Florida Atlantic University. These octopuses may use silt and shells to defend their territory or inform potential mates that they are not interested in a mate.

For example, researchers observed a female octopus hitting her male neighbor five times with silt over the course of approximately four hours. This was after he had failed several attempts to mate with her.

Regardless of what motivates this behavior, the fact gloomy octopuses engage in it at all sets them apart from the majority of animals. Only a few animals have been known to throw things. A smaller number of animals, all of which are highly social mammals, have been known to throw things at other animals.

Octopuses generally have been thought to live solitary lives. However, the discovery that gloomy octopuses are undersea snipers is one of several recent revelations about the social lives of octopuses that suggest these highly intelligent creatures may be more social than previously thought.

“With the advancement in technology, we are able to capture more of the underwater world and understand the fascinating behaviors of the most intelligent invertebrate,” says Bennice. “I look forward to seeing what additional videos can reveal.”