‘Tool user’ octopus carries and hides in coconuts

After humans, other primates and birds, octopuses have joined the growing list of tool users—they carry coconuts.

The veined octopus under study manages a behavioural trick that the researchers call stilt walking.

In it, the soft-bodied octopus spreads itself over stacked, upright coconut shell "bowls," makes its eight arms rigid, and raises the whole assembly to amble on eight "stilts" across the seafloor.

The only benefit to the octopus's ungainly manoeuvre is to use the shells later as a shelter or lair, and that's what makes it wholly different from a hermit crab using the discarded shell of a snail.

"There is a fundamental difference between picking up a nearby object and putting it over your head as protection versus collecting, arranging, transporting (awkwardly), and assembling portable armour as required," said Mark Norman of the Museum Victoria in Australia.

Julian Finn, also of the Museum Victoria, said the initial discovery was completely serendipitous.

"While I have observed and videoed octopuses hiding in shells many times, I never expected to find an octopus that stacks multiple coconut shells and jogs across the seafloor carrying them," he said.

Finn recalled the first time that he saw this behaviour, and said: "I could tell that the octopus, busy manipulating coconut shells, was up to something, but I never expected it would pick up the stacked shells and run away. It was an extremely comical sight—I have never laughed so hard underwater."

The researchers observed the behaviour of 20 veined octopuses after 500 diver hours spent "under the sea”.

On four occasions, individuals travelled over considerable distances—up to 20 meters—while carrying stacked coconut shell halves beneath their body.

"Ultimately, the collection and use of objects by animals is likely to form a continuum stretching from insects to primates, with the definition of tools providing a perpetual opportunity for debate. However, the discovery of this octopus tiptoeing across the sea floor with its prized coconut shells suggests that even marine invertebrates engage in behaviours that we once thought the preserve of humans," the researchers concluded.

The study has been published in the latest issue of Current Biology, a Cell Press publication.