There’s a great octopus story coming your way tomorrow. For that reason, I thought it was about time to republish this – the first ever post I wrote for Not Exactly Rocket Science, about the ever-amazing mimic octopus. This article was a game-changer for me. I submitted it to the Daily Telegraph’s Young Science Writer competition in 2004, while still struggling with a failing attempt at research. It was awarded a runner-up prize – not a win, but enough to convince me that I could actually write and that I enjoyed it. Looking back on it now, it’s decent but a bit rough. It also took forever to write – today, I crank stuff like this out in a an hour. But I’m still fond of it – this was the piece that started a career.

As you swim through tropical waters, you notice that a strange creature has entered your territory. The intruder is unfamiliar, but when you try to chase it away, it undergoes a startling transformation. Its new form is one you recognise – a banded sea-snake, highly venomous and likely to make you its next meal. You turn and flee. You are a damselfish, you are in Indo-Malayan seas, and you have just been duped by the mimic octopus.

The mimic octopus is new to science and has yet to be properly classified [NB - Since 2004, the octopus has been classified as Thaumoctopus mimicus - the "mimicking miracle octopus" - Ed]. It has, though, already gained notoriety for its unique ability to impersonate venomous or distasteful animals. Politicians and pop-stars may be beyond its scope, but its repertoire includes soles, lionfish, sea-snakes, and possibly sea anemones, stingrays and jellyfish.

To transform into a sea-snake, for example, the octopus withdraws its head and six of its tentacles into a burrow and waves the other two in opposite directions in an uncannily serpentine manner. You can download some Quicktime videos of the octopus doing its thing from the Royal Society website.

Octopus specialist Dr Mark Norman, from the University of Melbourne, Australia, first observed the mimic off the coast of Indonesia. There, it forages in open sand flats during broad daylight and its talents may have evolved to keep it safe in these vulnerable surroundings. As Norman says, when you’re caught in the open by a passing fish, “you’ve got to look either deadly or inedible”.

Mimicking deadly or inedible animals reaps obvious benefits – predators avoid you, and you need not bother making poisons yourself. It has therefore become a common strategy, used by snakes and flies, spiders and plants. But these charlatans are all one-trick ponies.

In comparison, the mimic octopus’s charades are orders of magnitude more dynamic. “No other animal has been found that is able to rapidly change between different forms of mimicry”, says Dr Tom Tregenza, from the University of Leeds, UK, co-author of the paper which first described the mimic.

Having multiple acts benefits the octopus as predators are less likely to catch on to any individual one. If too many octopuses mimic a single creature – say, a lionfish – then predators are more and more likely to encounter the fake than the real deal. They might never learn that something that looks and moves like a lionfish is not worth biting.

Like all good performers, the mimic octopus caters to its audience. It only acts like a sea-snake (right) when confronted by territorial damselfish, which are preyed upon by sea-snakes. “This is very exciting because it raises the possibility that the mimic octopus can employ different forms of mimicry to counter different threats”, says Tregenza.

But is the mimic actually mimicking or are human eyes misinterpreting these movements? To answer this, a BBC/Discovery film crew captured six hours of live footage of the mimic in 2000. The combination of colour, posture and very “un-octopus-like” movement convinced many sceptics.

For example, when mimicking the leaf-shaped sole, the octopus not only draws its tentacles and head back into a leaf shape, but also matches a sole’s colours and undulates its body to resemble its swimming style.

Norman believes that octopuses as a group are the equivalent of “rump steak swimming around”. Their bodies lack any sort of protective shell or skeleton and they have had to evolve other incredible defences to compensate. Soft bodies make them vulnerable, but they also make octopuses particularly well-suited to deception.

Without skeletons, they are expert contortionists, and can change shape or squeeze into tight spaces. Their remarkable skin can change texture, becoming spiky or smooth on a whim. It also contains sacs of pigment called chromatophores which can be expanded or contracted to produce rapid changes of colour and pattern. Armed with this arsenal of stealth, all octopuses are masters of disguise.

Most species are content to blend into their backgrounds. The mimic’s ancestor probably lived unnoticed in nearby coral reefs. These reefs are like busy and crowded high streets; in contrast, the sand flats are an open market, with rich pickings for any animal (provided that they can avoid being eaten).

The octopus’s inbuilt camouflage abilities would have given it a head-start. As time passed, individuals that slightly resembled poisonous animals would have lived longer without being eaten, allowing them to pass their appearances on to their offspring.

The mimic’s behaviour remained undiscovered for years because its dull homelands are poorly studied. But it is precisely this barren nature that has provided the impetus to evolve such amazing behaviour.

As Tregenza says, “The mimic octopus teaches us that very bland and barren habitats may be home to the most impressive behaviours.” Even more surprising and wondrous animals may await discovery in these unexplored worlds.

More cephalopods:

• Glowing squid use bacterial flashlights that double as an extra pair of “eyes”
• What the stomach contents of sperm whales tell us about giant squid and octopuses
• Cuttlefish tailor their defences to different predators
• How to tell Wonderpus Joe from Wonderpus Bob
• Camouflaged communication – the secret signals of squid
• Cuttlefish learn from watching potential prey even before they are born

December 13th, 2009 Tags: mimic octopus
by Ed Yong in Animal behaviour, Animal defences, Animals, Cephalopods, Invertebrates, Mimicry | 5 comments | RSS feed | Trackback >