We still know precious little about the lives of most octopus species, and it was only in 2009 that experts discovered they could use 'tools'. Now this extraordinary tool-using ability has been filmed for episode two of BBC's Life Story.
Here are seven amazing things you never knew octopuses could do.
1. They use coconuts as tools
Octopuses are known for their intelligence, but it was only five years ago that scientists recorded the first-tool use among these cephalopods: underwater footage showed veined octopuses (Amphioctopus marginatus) in Indonesia collecting coconuts to use as shelters at a later date.
The crew of BBC One’s Life Story captured the unusual behaviour on camera for the programme. In the sequence, an octopus grasps a coconut half in its arms and scuttles off to find another half. It then encloses itself in a self-made protective shell. This allows the soft-bodied creature to hide from predatory cuttlefish. The coconuts can even be used as a getaway vehicle – the octopuses can roll away from danger, safe inside the shell.
2. Female octopuses go to extra lengths
Female octopuses can stretch their arms further than males of an equivalent size, scientists studying the animals’ biomechanics in Italy revealed in 2013. They tested octopuses’ arm elongation abilities in a tank: the cephalopods had to reach up a tube and straighten their arms to reach tasty bait. The study also found all the octopuses tested could extend their arms over twice their normal length.
In the wild, octopuses use their appendages for a range of activities such as cleaning themselves, defending against enemies catching prey and mating.
3. Octopuses have a special arm for mating
During mating, the male octopus uses its “hectoctylus” to insert sperm into the female. Male octopuses might only use the hectoctylus for the purpose of mating, and they have been observed holding this specialised limb close to their bodies while foraging in the wild, possibly to protect it.
4. The Indonesian mimic octopus pretends to be a fish
Indonesian mimic octopuses (Thaumoctopus mimicus) are masters of disguise: they have the amazing ability of passing themselves off as the toxic fish species or sea snakes with which they share their habitat, in the hope of scaring off predators. For example, by flattening their heads and arms and displaying a brown and white pattern the species mimics a poisonous flatfish. It even copies the fish’s swimming movements for extra effect.
In a strange twist, researchers have discovered a fish that copies these octopuses’ mimicry. Scientists from the University of Gottingen, Germany recorded a black marble jawfish acting as an “opportunistic mimic” in the octopus’ tentacles to protect itself from predators too while it foraged for food.
5. Bizarre octopus secretes its own shell
The female argonaut secretes a very thin shell made of calcium carbonate around itself, using web structures on the sides of its body. These shells, which are unique to the species, allow the octopuses to release trapped air, which allows them to control precise movements through the water. While female argonauts can grow up to 50cm in length, males are tiny – typically reaching only a centimetre in length.
6. They make the ultimate sacrifice for love...
Male octopuses die within a few months of mating and most females perish not long after tending to their thousands, or even hundreds of thousands of eggs. However one deep sea octopus was recorded guarding her eggs for an astounding four years and five months - the longest brooding time ever recorded in an animal.
7. ...But one individual was seen strangling her mate
A female common reed octopus living off Fiabacet Island in Indonesia stunned on-looking researchers when she strangled her male lover immediately after mating with him. The behaviour is extremely rare among octopuses, which are rarely aggressive. The gruesome encounter entailed the female lunging and grabbing the smaller male with two arms and strangling him until he stopped moving, before dragging the unfortunate octopus into her den, possibly to devour him.
Watch a veined octopus in action in episode two of Life Story at 21:00, Thursday 30 October, BBC One.