SCIENCE -ARMS- SPECIAL : OCTOPUS

Up In Arms : When an octopus gets so mad it wants to throw something.

The urge to hurl something when irritated is not confined to land animals. A study published in the journal PLOS One shows that octopuses of at least one species throw silt and shells - sometimes at one another.

While octopuses are intelligent, most species live largely solitary lives. But in Jervis Bay, Australia, unusually large numbers of one species - Octopus tetricus, or the gloomy octopus - gather at sites nicknamed Octopolis and Octlantis.

Ideal den conditions and abundant food attract the antisocial animals and draw them into close quarters, where they often poke, prod, grab and otherwise annoy one another. And that can lead to the deployment of projectiles.

Researchers observed this behavior while poring over video taken near octopus dens.

Though the researchers call the octopuses' actions ''throws,'' Jervis Bay is not like a dodge ball court : In only one case did an octopus fling a shell by straightening its arm as a human would.

There isn't really a word for what the gloomy octopus does. For instance, if one feels provoked by its neighbor, it will gather silt. When ready to fire, the thrower positions its siphon - the tubular organ used to pump water for swimming - to push the debris outward. [Darren Incorvaia]