杏吧原创

Octopuses have been recorded gathering up armfuls of debris 鈥� and remember, they have eight arms 鈥� before taking pot shots at one another. Whether it鈥檚 a case of 鈥済et off my turf鈥� or merely 鈥渙ops, didn鈥檛 mean to hit you鈥� is still a puzzle.

Octopuses have siphons on the side of their body, which they normally use for jet propulsion 鈥� they expel water forcefully through them, shooting forward as a result.

Gloomy octopuses (Octopus tetricus) living on a bed of shells at Jervis Bay, Australia, seem to have co-opted this system to throw things at each other in what may be the first use of projectile weapons seen in octopuses.

鈥淰ery few animals have been reported to throw things at one another, so it would be significant if the octopuses are doing it鈥�, says , a聽professor of philosophy聽at the Graduate Center, City University of New York, who presented video evidence at the in Cairns, Australia, this month.

Enthusiastic housekeeping

The technique the gloomy octopus uses seems to be a throw helped with a spit (see video above).

鈥淚n the 鈥榯hrowing鈥� behaviour, it gathers up a pile of stuff in its arms, and then directs the jet under the web of its arms, and throws out all the stuff under pressure,鈥� says Godfrey-Smith. 鈥淪o it鈥檚 a throw rather than a spit, though the throw uses water pressure 鈥� it uses a sort of inverted jet propulsion.鈥�

Godfrey-Smith is not yet certain that the behaviour is intentional. It may just be a case of enthusiastic housekeeping showering the neighbours with debris.

鈥淥ctopuses often clean out their homes with a jet of water, pushing out sand and rubble. They also jet at intruders like pesky fishes,鈥� says , a behavioural ecologist from the University of Lethbridge in Alberta, Canada, who was not involved in the study.

However, other octopuses were hit with the debris more often than you would expect by chance.

Eight-armed boxing

If indeed it is intentional, it may have evolved as a response to unusually crowded conditions at Jervis Bay.

The octopuses live on a midden made of shells, where they excavate dens. But with each octopus only having an area around a meter square to themselves, their neighbours can be as close as 30 centimetres away.

This is not the ideal living arrangement for solitary octopuses. But they probably put up with it because of overabundance of scallops 鈥� their favourite food 鈥� and a lack of other suitable nesting sites.

Even without the throwing behaviour, the crowding has brought out the worst in the inhabitants, it seems. A large female-male pair was caught on camera, for example, fighting intermittently for almost 2.5 minutes. Another time, a large octopus bullied a smaller one into leaving its den.

The team also observed many , where two octopuses probed rapidly at each other with their arms (Marine and Freshwater Behaviour and Physiology, DOI: 10.1080/10236244.2012.727617).