Octopuses ‘walk’ on 2 arms to get by predators

While pigs are not yet flying, coconuts are walking and clumps of algae are tiptoeing — sort of. The coconuts and clumps of algae are really octopuses walking on two arms and using their six non-walking arms to camouflage themselves as plant material in order to hide from lurking predators.

These octopuses are the first animals without a hard skeleton known to walk on two limbs. Octopuses normally travel along the ocean floor using all or many of their eight arms in a sort of crawl. Their muscles are supported by fluid and not bone. Using underwater video, the scientists analyzed the strides of Octopus marginatus and Octopus aculeatus. For both species, each walking arm stayed in contact with the sandy ocean floor for more than half of the stride, qualifying the pitter patter of two octopus arms as official walking.

These findings appear in the 25 March, 2005 issue of the journal Science published by AAAS, the nonprofit science society.

“It wouldn’t surprise me if other octopus species also walk,” said Science author Christine Huffard, from the University of California, Berkeley.

Huffard observed octopuses seemingly impersonating coconuts in Indonesia and octopuses walking like floating algae in Australia. She explained that many octopus species around the world have strong, muscular back legs that could be used for walking on two limbs.

'Impersonating' plants

FREE VIDEO Posing as algae March 24: An Octopus aculeatus walks backward on two arms while using its other arms to mimic a piece of algae. Christine Huffard

By walking on only two arms, the other six arms can be used to transform their bodies into clumps of algae or rolling coconut shells that may not interest predators. Clumps of algae and coconut shells are commonly found in the shallow, coastal seawaters that these octopuses call home.

Octopus predators such as sharks, sting rays, predatory reef fish and flounder scan the sea floor for creatures doing the traditional “octopus crawl” which involves the octopus pushing and pulling its body along the ocean floor using many of its eight arms.

By shifting to a camouflaged walk, the octopus may slip past their predators’ octopus-detection schemes without having to stand still. Camouflaged walking -- always in the backward direction and on the back pair of legs -- is probably hardwired into their brains as well as their arms.

When threatened by a predator, something kicks in and the octopuses start walking without consciously thinking, “I need to move the right arm and the left arm,” Huffard explained.

MORE FROM SCIENCE MYSTERIES

Science Mysteries Section Front

Rebuilding wetlands: Do hurricanes help? Tiny shells may be world’s oldest beads Can evolution make things less complex? Olive branch solves a Bronze Age mystery Artificial muscles get a makeover The why behind a wine’s bouquet Humans hard-wired for geometry Fish help unlock mystery of skin color Animal eyes inspire new technology Science gets the last laugh on ethnic jokes Science Mysteries Section Front   Add Science Mysteries headlines to your news reader: