Smashers & Spearers
I FOUND MYSELF LAUGHING through my regulator in sheer delight. Delight at the oddness, the sheer improbability of this scurrying little killer, from the stunning iridescence of its gaudy colours to the bantam-rooster, chest-out strut of its fore-body, to the feverish train-set scurry of its long, low body and abdomen.
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 shrimps must be at the top of the “weirdness charts”, however.
The mantis, often up to 30cm long, looks to have been built from odd-sized spare parts, yet it somehow flows together extremely well. The basic bodyplan is classic crustacean – like crabs, lobsters and shrimps – but the proportions of the limbs and segments don’t quite look right.
The carapace is small and skinny. Unlike on crabs and lobsters, it neither covers the head nor very much of the body.
The rear part of the body, and the last three pairs of walking legs, blend into the long, locomotive-like, or perhaps centipede-like, armoured tail. Movement over the reef is almost a fast glide, but is driven by the furious beating of the eight pairs of double legs and swimmerets.
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.
He stopped once in a while to inspect his surroundings, fixing me with the gaze of one
of his three-lobed, alien eyes as the other swept around behind him. Each is a compound eye
like an insect’s, but the dark, focusing sets of cells within each iridescent eye followed me, hinting at a vision – and an intelligence – that is much more complex.
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.
As mere humans, it is difficult even to conceptualise how mantis shrimps see the world.
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.
Championship boxer Ricky Hatton has been measured with a punch speed of up to 35mph, and up to 400kg of force – twice as fast and several times more powerful than most of the rest of us. An Internet search brings up martial artists discussing Bruce Lee being perhaps even a little faster.
A mantis shrimp is faster than either, and 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. The oft-repeated comparison with a .22 bullet, and the tales of mantids shattering aquarium glass or splitting thumbs, are valid for exactly this reason.
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.
The shimmering, transparent or reflective adaptations of their prey to evade capture make their vision that much more important. They are simply the baddest kid on the reef.
They have been seen killing triggerfish – normally the scourge of small crustaceans – and even beating blue-ringed octopus literally to a pulp, keeping their distance while the cloud of toxin disperses from the mangled octopus before they tuck in.
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.
Male peacock mantises especially are vividly painted in greens, turquoise, reds, orange, browns, whites and blacks. The females are slightly more muted, but they all fluoresce, the females in particular when they are ready to mate and spawn, around the full moon. (They mate in the missionary position, with paired, erectile penises, apparently!)
Courtship rituals ensure that the “make love not war” message is understood. Combine this social need with the shallow, bright, complex reef habitat in which they live, and the multi-faceted, multi-filtered eyes of mantids make sense.
Unlike other crustaceans, mantis shrimps have large brains, long lives (up to 40 years) and complex behaviours, 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 (and few vertebrates) have such complex behaviour.
I watched a dive guide and tourists baiting a giant sandy brown Lysiosquillina at its burrow in Lembeh. The burrow wasn’t much bigger around than my wrist, but as the shrimp rose out to challenge the intruders and its wickedly spined undercarriage unfurled slowly, ready to strike, you could see that this monster must have quite a reach. I was a little disappointed that he didn’t teach his tormentors a lesson.
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.
Back in Lembeh, my particular peacock smasher shrimp had had enough of me trying to position myself for a good photo.
After a couple of tries to move out of his sight, and some peekaboo around various coral heads, it became apparent that he could effortlessly both anticipate and outmanoeuvre me.
He let me take a couple of portraits; then he simply vanished.