Nature’s hardest oddball has the most powerful punch on Earth, but it is stunning in other ways too, according to marine biologist JAMIE WATTS
You normally glimpse mantis shrimps retreating into crevices or running away, but this guy was cruising over the reef, a mix of curious self-assuredness and nervous hurry.
We were fulfilling a long-term dream of diving in the Lembeh Strait in Indonesia. It certainly lived up to the hype, and we had seen dozens of the strangest, most delightful little creatures in the world.
The mantis, often up to 30cm long, looks to have been built from odd-sized spare parts, yet it somehow flows together extremely well. This fluid glide over and around obstacles, punctuated by freezing to absolute stillness of everything but the huge, constantly rotating, stalked eyes, makes me think of Randall Boggs, Steve Buscemi’s chameleon-like amphibian from Monsters Inc.
SUPER VISION
The compound eyes are regarded as the most complex and capable eyes on Earth. Their three sections give trinocular vision with each eye – better than our binocular vision. The wide separation and independence of each eye not only doubles this to give the mantis six-way (sex-nocular!?) vision, but allows each set of three eyes to scan independently all around, while keeping incredible focus and acuity. It doesn’t even end there. We see in three colours – basically red, green and blue – whereas the mid-band in each mantis-shrimp eyeball can see in 10 colours, including ultra-violet, infra-red and polarised light.
PUNCHING WELL ABOVE ITS WEIGHT
How mantis shrimps use this vision, or why they need it, is not totally understood. One reason is certainly a need to judge their legendary punch. Mantis shrimps have the most powerful physical weapon for their size of any animal. Without precise distance estimation, the mantis could either yank off its own limbs by striking in front of a target, or smash them by punching through something excessively solid. The punch (a kick, if we’re being pedantic) of a mantis shrimp is 10 times faster than the strike of its land-based namesake, the praying mantis. A mantis shrimp can punch at more than 50mph, with 150kg of force. This is about the same force as a fit young adult human can muster in a punch, but focused into a tiny point of contact.
Even more impressive is that this force is generated through water. The unfortunate victim gets hit twice – first by the blow, then by the shock wave from the speed of the punch instantly boiling the water. This shock wave can kill the prey even if the blow misses, and is powerful enough to emit a flash of light. The second leg – the punching leg – is rather like a human leg in build, with the power coming from the “thigh” muscle. The equivalent of the knee is tucked under the chin, and the “foot” is either a sharp-edged club or a series of long curved spines, depending on the species.
There are around 425 species of mantis shrimp, separated into “smashers” or “spearers” by their foot design. Either way, they have a latch between the thigh and the knee, building up tension in a curved leaf-spring before releasing the latch – and the punch.
Mantis shrimps are merciless and vicious in attack, with smashers pummelling the shells of crabs and snails to pieces, and spearers shooting out their wickedly elegant long limbs to impale fish and cuttlefish.
A COMPLEX LIFE
There is, however, a more sophisticated side to these creatures. The vivid purple and blue target painted on the tail-fan of the commonly seen Indo-Pacific peacock smashing mantis hints at another reason for that incredible vision. Because they fight over a limited supply of small living space, and over mates, and because of their incredible ability to do damage, like many aggressive animals mantis shrimps need a mechanism to make sure that each fight does not necessarily end in death.
So they literally give each other a vividly painted target on their tail-shield to attack – they can then strike a strong-enough blow to give a clear indication of strength without having to kill each other. They sometimes even bluff, holding out the flaplike antenna scales to startle off another mantis, even when they are newly moulted and soft-bodied.
Unlike other crustaceans, mantis shrimps have large brains, long lives (up to 40 years) and complex behaviour, including recognising individuals, courtship and elaborate ritualised fights over mates.
At least in the case of Lysiosquillina maculata, a giant spearer and the largest mantis shrimp, occasionally exceeding 40cm in length, this behaviour extends to long-term monogamous relationships. No other invertebrates have such complex behaviour.
Many of us tend to think of mantis shrimps as tropical, but they are surprisingly abundant in cooler waters. The Med has a fishery for one spearer, and at least one smaller version of the giant tropical spearer is not uncommon around western and southern coasts of the UK. Rissoides desmaresti lives in burrows on sandy bottoms, and has been seen over extensive areas off Wales in particular. The size of a king prawn, apparently our resident spearer is every bit as pugilistic as its larger tropical cousins.