Invertebrates
Coconut Octopus
Amphioctopus marginatus · also called coconut octopus, veined octopus
The coconut octopus lives on bare sand and mud, with no reef to hide in, so it carries its shelter with it. It collects empty coconut shell halves — or, where there are no coconuts, large clam shells — stacks them under its body, and stilt-walks across the seabed on two arms, gear in hand. When something threatens it, it climbs inside and pulls the halves shut like a clam. Carrying a tool around for later use is one of the clearest examples of intelligence ever shown in an invertebrate.
Overview
The coconut octopus lives on soft seabeds of shallow bays and lagoons across the tropical western Pacific and eastern Indian Ocean, not on coral reefs. It is small — a body of about 8 cm, arm span 15 cm — brown to grey, with a network of darker “veins.” It hunts crabs, shrimp, and small clams at night.
A portable home
On open ground it gathers shell halves, keeps them, and when danger appears climbs inside and pulls them shut. To move them, it stacks the shells beneath its body and walks backwards on the stiffened tips of two arms — carrying protection it does not need at that moment for a threat it anticipates.
A landmark study
A 2009 study of coconut octopuses filmed off Indonesia was widely accepted as the first clear demonstration of tool use by an invertebrate.
Independent intelligence
Octopuses are molluscs — closer to clams than to any vertebrate — and their intelligence evolved completely independently of that of mammals and birds.
Status
The coconut octopus has not been assessed. It is widespread on suitable habitat, with trawling and the aquarium trade the main pressures.
Coconut Octopus: common questions
Does the coconut octopus really use tools?
By the standard definition used in animal behaviour, yes. Tool use means holding or carrying an external object and using it to achieve a goal, and the strongest version of the claim, transporting an object for future use rather than using something that happens to be at hand, is exactly what the coconut octopus does. It selects shell halves, cleans them out, stacks them, and carries them across open seabed where they provide no benefit at the time, then deploys them as a shelter when a predator appears. The 2009 paper that documented this in detail is generally cited as the first clear case of tool use in any invertebrate.
Why coconut shells?
Coconut shells are a relatively recent addition. Before people were discarding coconut halves into tropical seas, the octopuses used the shells of large bivalve molluscs, which do the same job, and they still do where coconuts are scarce. What the octopus needs is a pair of hard, curved, roughly hemispherical objects that it can fit inside and pull together to form a closed sphere. A coconut cut in half by a person, then thrown overboard, happens to be an almost perfect ready-made version, so on seabeds near coastal towns the octopuses have largely switched to using them.
How does it walk while carrying its shells?
With difficulty, and slowly. The octopus tucks the stacked shells against the underside of its body, using several arms to hold them in place, and then extends the stiffened tips of the remaining two arms down to the seabed and rolls along on them, so that its rounded body is carried above rather than dragged. This gait is clumsy and leaves the animal exposed, which is a genuine cost, and the fact that the octopus accepts that cost to keep its shells with it is part of why the behaviour is regarded as forward-planning rather than simple opportunism.
How intelligent are octopuses generally?
Octopuses are the most behaviourally complex invertebrates known. They have large brains for their body size, most of the neurons distributed through the arms, and they show observational learning, problem-solving, individual personalities, and, in the case of the coconut octopus, tool use. This is remarkable because octopuses are molluscs, more closely related to snails and clams than to any vertebrate, and their intelligence evolved completely independently of the intelligence of mammals and birds, from a common ancestor that lived over 500 million years ago and had nothing resembling a complex brain.