MY RESPECT FOR SQUID – tinged with the fear of the unfamiliar – began years ago in the Red Sea’s Na’ama Bay.
Snorkelling on a moonless night, away from the lights of what was then a small town, my torch-beam picked up a squid a little way offshore.
Not wanting to scare it, I glided smoothly and slowly out over deep water. I needn’t have worried. The squid held its ground, and as I edged the beam towards it, it erupted in flashes of greens, blues, browns and oranges.
Its girth was a little bigger than my arm, it was as long as my leg, and from what I’ve been able to find out since, it was probably a rather large Loligo, one of an abundant group of inshore squids.
I was just over a metre away, looking at the unreadable, lidded iris, trying not to spook it and wondering if it would ink me as it ran away, when I was given a lesson in attitude.
The squid turned towards me, and suddenly its arms were raised and its tentacles poised to strike, as it flashed and flushed alarmingly.
Everything about this situation was at odds with the world I knew – the blackness around me, the depth beneath me, and my one point of reference beyond the edge of my comfort zone was an angry alien mass of glowing and flashing colours. The world I thought I knew suddenly didn’t make sense.
I backed away hastily – if I had a tail, it would have been between my legs.
There’s something deliciously compelling about anything as alien, ugly, beautiful and perhaps dangerous as squid, octopus and cuttlefish – the cephalopods.
Squid stand apart from their low-energy, bottom-dwelling cousins the octopuses and cuttlefishes. They are the spartan warriors of the seas, the one group of invertebrates that dares to rise into open water and take on the most advanced marine predators on Earth. And the squid may even be winning.
There are only around 300 species of squid. This is fewer than those of sharks or rays and a tiny fraction of the number of bony fish species.
If success is measured in terms of sheer numbers and combined mass, however, squid are far more successful than their closest ecological competitors the sharks, and many times more successful than their nemeses, the energy-hungry marine mammals.
Indeed, squid are the only serious competition to fish for dominance of the upper end of ocean food-webs.
In the past century we’ve done a pretty good job of stripping back medium-to-large fish populations, removing the competition and paving the way for the squid to dominate.

SQUID ARE KNOWN FOR FLASHING deep reds and occasionally other colours, although their repertoire can’t match those of their cousins the octopuses and cuttlefishes.
The colour changes are made possible by the top layer of the white skin, which has hundreds of coloured cells (chromatophores) embedded in it.
If you look closely at the skin of a cephalopod you can see these individual pixels, which give the skin a grainy look.
Each cell can be squeezed to a pinprick by muscles in the white skin, or opened out and enlarged to a big vivid spot.
Different arrays in the skin give each squid a repertoire of five or so basic colour patterns. They lack the octopuses’ and cuttlefishes’ wider range of patterns, and their ability to change the texture of their skin to any significant degree.
The colour signalling of most squid is limited to angry dark red flashes, which squid themselves, lacking colour vision, see as shades of grey.
Shallow-living squid have mirror-like cells deeper in their skin, so can reflect green, blue and gold iridescent sheens.
The tiny deep-sea firefly squid puts on spectacular light and colour shows, including luminous flashes of several colours, and has evolved complex colour vision – unlike that of any other cephalopod – to go with them.
The skin patterns are used to confuse and startle predators and prey, to attract mates and to communicate in a very simple visual language something along the lines of “please don’t eat me, let’s have sex instead”.
This is pretty important in fast aggressive species in which other members of the shoal, rather than fat storage, are the communal food reserve for lean times.
As several males are often drawn to the same female during the one short mating season these animals ever have, a male may well have to signal to the female and at the same time be transmitting coloured threats to see off rivals.
If startling and confusing with colour doesn’t work, then as divers and would-be predators have discovered, the animal can occasionally vanish behind a thick burst of ink.
Apart from confusing the vision, this can cause misleading or irritant smells and tastes, and may even act as an acoustic decoy to dolphins and sperm whales.

EVEN BY CEPHALOPOD STANDARDS, squid are fairly simple physically.
They are spindle-shaped muscle-bags with a funnel under the chin for jet propulsion and fins at the rear for regular cruising, blending smoothly into a head with eight arms, with two long tentacles retracted inside them, ready to shoot out like a chameleon’s tongue to grab prey at quite some distance.
I once watched a small Caribbean reef squid glide towards an unsuspecting fish almost its own size, and strike from two body-lengths away.
Squid have the fastest reflexes on Earth, more powerful musculature than almost any other animal and perhaps the most formidable armaments of any predator. Unlike the smooth “bath-mat” suckers on the tentacles of octopuses, squid suckers have lots of literally razor-sharp teeth.
As fast-moving predators in three dimensions, squid have complex balance sensitivity, and vibration-sensitivity similar to the lateral lines of fish.
They do not have the octopuses’ advanced sense of taste, nor the cuttlefishes’ vocabulary of displays, and lack the large brains and complex behaviour of their cousins.
Neither do any of them, as far as we know, have venom glands, as many octopuses and cuttlefish do.
They go for brawn, speed and aggression over sophistication.
This fast, reactive and predatory mass of muscle and nerves gets pretty scary from a diver’s perspective in a handful of squids. About a dozen species, mainly from cold or deep waters rarely seen by divers, grow larger than a small dog, and at this size diving with them can become terrifying.
Fishermen have long known the Baja jumbo or Humboldt squid as diablo rojo – the red devil – and many divers have been slammed, grabbed and startled by them.
There have been a few sprained limbs, grabbed masks and regs, and at least two divers have been reported killed, with squid as the main suspects.
However, most divers report a fascination with the mesmerising colour flashes, and the slightly shy, nervous but curious behaviour of the squid.

CEPHALOPODS ARE REMARKABLE in the briefness, intensity and efficiency of their short lives. Most live only a year, but in that time they become impressive predators, growing faster than any other complex animal. The secret is an incredible ecological conversion efficiency; the proportion of the food that is converted to body mass. If you like calamari, you can rest assured that the meat was produced far more efficiently than fish, beef or even chicken.
A handful of large coldwater cephalopods live up to three or four years, compared to the 20 or more for large fish, sharks and mammals, but because of their food-conversion efficiency, in that short time they can become giants.
One side-effect of such rapid growth is the need to change the prey chosen. Small cephalopods prefer crustaceans – shrimp, crabs etc – but larger species quickly work their way up the food web, out-growing successive types of prey.
A fish that may be a dangerous predator to a young squid may become a tasty morsel a few weeks later.
In some cases this may be what limits the growth of large cephalopods – they run out of a choice of things to eat. Colossal squid attack hooked toothfish
as big as a human from longlines.
The downside to this rapid growth is that their protein-based metabolism demands a constant supply of food.
Squid are not built for storage or lean periods. They have to keep moving to where there is ample food, so are found in numbers only in cool, rich seas.
Squid move in larger groups than other cephalopods, and sometimes migrate long distances.
Migrating en masse gives them a handy reserve for lean times – jumbo squid and others cannibalise the smaller members of the school in the absence of alternative food on the way to the spawning grounds.

I HAD THE OPPORTUNITY to examine what may well be the largest specimen (albeit partial) ever found of the colossal squid, Mesonychoteuthis hamiltoni.
The tapering arms were as big around as a human arm, and a little over a metre long – shorter than those of the giant squid but much thicker and more muscular.
These arms surrounded the grapefruit-sized beak mass, and near the bases and the tips had simple suckers on stalks edged with small serrated teeth. These suckers alone cut small cookie-chunks from prey, but the middle of each arm has even more fearsome suckers.
These are again stalked, but offset, hanging away from the mouth and about the size of the end of a thumb. Each sucker has an inward-hooked tooth at the end and a smaller one either side, and so is basically a hook. The only way in which prey too weak to tear off the muscular arms can go is towards the beak.
As if this metre-long cone of death – effectively a massive mouth – was not enough, the two tentacles were nearly 2.5m long. In the living animal they may well have been able to shoot out and grab prey 4m from the mouth.
At the end of the tentacles were tentacle clubs, armed not only with even more of the pivoting, hooked suckers but with press-stud-like suckers and knobs designed to clamp the clubs together around the prey. This 8m giant is the largest and most powerful species of squid, but most squid are similarly armed, albeit on a smaller scale.
The giant squids may not be large enough to drag down ships, like the kraken of legend, but they are spectacular predators. They are also far more abundant on a global scale than other large predators such as dolphins, sharks and large fish.
Despite our failure to find live colossal squid (and divers are unlikely to meet them as they live deep below the roughest seas on Earth around inaccessible Antarctica) we know from the diet of sperm whales that this is one of the most abundant large animals, with literally millions of tonnes of biomass.
Longer but much less heavily built is the rare and still-elusive giant squid Architeuthis, found (very occasionally) almost worldwide.
Architeuthis has been recorded to 12m in length (most of which is the super-elastic tentacles) but is less than half the bulk of the colossal squid and a much less impressive predator, unless reports of 18m giants can be verified.
Scott Cassell, who has worked and dived with jumbo squid for years, attached a low-light camera to a dog-sized jumbo squid recently and captured a few tantalising seconds of a huge squid apparently hunting the jumbos, with at least an 8m arm spread, which would fit about right with a 15m-plus Architeuthis.
Both of these giants, particularly the colossal, have soft bodies, at odds with their tough, muscular arms. These bodies are somewhat buoyant and designed for gentle drifting, perhaps lying in wait for prey rather than fast swimming.
As the first-ever footage of giant squid attacking a bait trap showed a couple of years ago, however, they can still be impressively fast, active predators.
Slightly smaller than these giants but more muscular-bodied and more active swimmers are robust clubhook squid from the cold north Pacific and jumbo or Humboldt squid from the east Pacific.
The former grows to the size of a large adult human, the latter a little smaller.
Both can be found in diving depths at night, and are rightly considered to be potentially dangerous and unpredictable diving companions. Divers sometimes wear shark-suit type chain-mail and are tethered to the surface.
Diving with these squid is not for everyone, but as they generally live in deep, cold seas and only come to the shallows at night in a few key areas, you have to be trying pretty hard to be anywhere near these giants anyway.