by Ted Dewan
‘Selkies’, the legendary Scottish seal women who leave their skins behind and are tricked into marriage by humans, may be a dim folk memory of visits by shaman from Lapland, who dressed in skins and used healing magic. ‘Seal’ is a Saami word.
With elephant seals, and their close relatives, the sea lions, this male aggression is also backed by huge size. The bigger and more aggressive the male, the bigger his bit of breeding beach and the higher the number of females he gets to service. A single male might have up to fifty females in his harem, but some harems grow as large as a thousand, serviced by just thirty males, with the top five – the ‘beachmasters’ – getting most of the action.
Much of the inter-male violence is just noise – loud gargling and slaps – but when fights do break out they can be bloody for both the participants and innocent bystanders. The females don’t help: they make such a racket during mating that every male in the area makes a beeline towards them. In the resulting melee, pups get separated from their mothers, and are crushed or flung out of the way. Some colonies lose two-thirds of the pups in a single season in this way. It is one of the reasons seals’ milk has the highest fat content of any mammal’s: to ensure the pups grow quickly. The milk is more of a pudding; at 60 per cent fat it’s twice as rich as whipping cream. Unsurprisingly, pups put on several pounds a day and are weaned within a few weeks.
It is in the sea that the seal’s strength and aggression really sets it apart. A seal hunting in water is twice as efficient as a lion on land. Elephant seals can dive for two hours at a time and reach depths of 5,000 feet. They expel all the air from their lungs to avoid the risk of ‘the bends’ and survive on the oxygen absorbed in their blood. Their bodies hold twice as much blood as most mammals and, when diving, their heart rate plummets from ninety to just four beats a minute. To help them sink faster, some will even swallow stones.
Better still, a seal’s eyes don’t go blurry underwater. In other mammals, this blur is caused by the outer lens (cornea) being rendered useless by the water, like a transparent glass marble which disappears when you drop it in the bath. Seals overcome this through a huge spherical inner lens to focus the image, and an extremely adjustable iris to control the light. This not only gives them their big-eyed charm, it also means they can hunt in bright sunlight and the gloomy ocean depths.
HOW TO TELL A SEAL FROM A SEA LION
Shark
Big girl’s blouse
Only one in a hundred shark species attacks people. In 2005, there were just fifty-eight shark attacks reported worldwide. Only four people were killed. Wasps kill as many people in Britain every year and jellyfish in the Philippines ten times as many. In the US, both dogs and alligators kill more people than sharks. To put it another way, in an average year in New York there are 1,600 cases of people biting people. Sharks have far more reason to be scared of us. We kill at least 70 million a year for food (despite the fact that some shark flesh tastes of urine, both ‘rock salmon’ and ‘huss’ are sharks) and for their livers (which are used in haemorrhoid cream).
If you turn a shark upside down it will go into a trance-like state called ‘tonic immobility’ for fifteen minutes. No one knows what causes it.
It’s a good job sharks find people a bit on the bony side and prefer seals. They are armed with a terrifying range of surveillance equipment. Two-thirds of a shark’s brain is dedicated to smell: it can detect blood diluted in water at strengths of one part in a million and from a distance of a quarter of a mile. Nor does lunch have to be bleeding for the shark to know it’s there. Shoaling fish exude chemicals to warn colleagues when danger threatens. Sharks intercept these signals, scenting fish that are not even wounded, merely nervous. A shark’s ability to detect low-frequency sounds means it can hear the very heartbeats of fish from far away, and pressure-sensitive receptors along its body allow it to ‘feel’ the remote movements of prey through the water. Cells under the skin of its head enable it to pinpoint tiny changes in magnetic fields and minute electrical impulses. These not only help it to navigate as if using a compass, but provide yet another killing aid: sensing individual muscle movements of a distant fish even when buried under sand. Some sharks even have a depth gauge in their middle ear. Equipped with this sophisticated gear, predatory sharks are able to hunt in total darkness.
Although in daylight they have perfectly good eyesight, these night raids must be their undoing. Items found in sharks’ stomachs include beer bottles, bags of potatoes, a tom-tom drum, car number-plates, house bricks, a suit of armour and a whole porcupine. A single tiger shark was found to have swallowed three overcoats and a raincoat, some trousers, a pair of shoes, a driving licence, a set of antlers, twelve intact lobsters and a whole hen-house full of partly digested chickens.
The female frilled shark holds the world record for the longest pregnancy in nature: over three years. The largest egg in nature belongs not to the ostrich but to the female whale shark. Discovered in 1953, it was 12 inches long, 6 inches wide and 4 inches thick. The embryos of female sand tiger sharks kill and eat each other in the womb. But since records began in 1580, fewer than 2,500 shark attacks on humans have been reported. This is equivalent to about 6 per cent of the number of Americans injured by lavatories in 1996 (43,687).
Male sharks do not have penises. Which probably explains a lot.
RADIOHEAD
Sheep
A thank-you note
Domesticated sheep (Ovis aries) may only exist because of humans – but we, in our modern form, only exist because of sheep. First domesticated in the Middle East and Central Asia around 9000 BC, some time after dogs, reindeer and goats, all modern sheep can trace their lineage back to two ancestral breeds, one probably extinct, the other, the tiny – and now endangered – mouflon (Ovis musimon). Sheep, even more than their close relatives the goats, were responsible for the greatest lifestyle shift in human history, the transition from hunter-gathering to farming. Goats were perfect for nomads, but sheep, because of their tendency to flock and their ability to graze on the toughest grass, allowed us to stay in one place. Sheep fertilised the ground they grazed on, allowing agriculture to flourish, and their flesh and milk gave us a break from hunting. To get the best out of sheep, they needed to be herded and guarded, leading to larger human settlements (and more work for the recently domesticated dog). Interestingly, the Latin for sheep, ovis, and the English ewe both derive from the Sanskrit avi, which has its roots in av meaning ‘to guard or protect’. Looking after sheep gave us civilisation.
It took 3,000 years for our ancestors to discover that by selectively breeding sheep they could encourage their fluffy undercoat to grow longer than the bristly guard hairs (called ‘kemp’). The result was first felt and then wool, and suddenly humans had yarn, then looms and textiles. If sheep farming was the first industry, wool became the first great trade commodity. By the Middle Ages, wool drove the economies of Europe: the Renaissance was largely financed on the profits from the wool trade. Today, synthetic fibres have dramatically reduced wool production in Europe and America: 60 per cent now comes from Australia, New Zealand and China.
Soay sheep from St Kilda, were isolated for 4,000 years and reverted to a feral state. They have to be peeled, not shorn, and stare in blank incomprehension at sheepdogs. All you need to keep them is a pair of binoculars.
Perhaps this apparent readiness to offer themselves up for our benefit has fed into their cultural role, which, historically, has been all about sacrifice. Unlike the more sexually suggestive associations attached to the goat, sheep have invariably found themselves being offered up in thanks, or having to symbolise innocent victimhood. The sacred texts of Judaism, Christianity and Islam overflow with lambs, flocks and shepherds. More recently, sheep have become a byword for conformism and stupidity, which is not only ungrateful but wrong. Far from being dim, sheep have good memories: they can recognise faces of other flock members and the face of their shepherd for up to two years. This facility has long been known by hill
farmers, whose flocks have become ‘hefted’ to a particular territory. Shepherds and dogs initially teach them which ridges, boulders and streams mark the grazing boundaries. The ewes then teach this to lambs and it gets passed on from generation to generation, sometimes stretching back hundreds of years. The loss of ‘hefted’ flocks was one of the hidden costs of the 2001 outbreak of foot-and-mouth disease, in which seven million British sheep were slaughtered. More recently, super-smart sheep have learned how to cross cattle-grids by taking a good run-up and then rolling up in a ball to cross them, SAS-style.
Snake
Happy eater
No one is born with a fear of snakes: it has to be learned. Even then it’s not really rational. In Florida, which is home to more than seventy different types of snake, 500 times as many people are bitten by dogs and far more people die from both bee stings and lightning strikes than from snakebites. The chance of being hurt in a road accident in Florida is at least a hundred times higher than that of being bitten by a snake. Snakes are not aggressive and do not chase after people. Even if they did, you’d just walk away. A rattlesnake travels at a top speed of 2 mph. The fastest snake ever recorded, a black mamba (Dendroaspis polylepis, ‘many-scaled wood snake’), clocked up only 10 mph.
Snakes have two penises hidden inside their bottoms. The one on the right is often larger, suggesting that they are ‘right-penised’ in the same way most humans are right-handed.
The smallest known snake is the burrowing thread snake (Leptotyphlops bilineata, ‘double-lined skinny blind-eye’). It is 6 inches long and as thin as a matchstick. No one knows how large the largest snakes are because the really big ones have never been brought back to be measured scientifically. At the beginning of the twentieth century, a reticulated python on the island of Celebes was said to be 33 feet long, and a green anaconda in Colombia reportedly measured 37.5 feet. No snakes as long as these have been reported for a hundred years. Snakeskin is so valuable that no snake survives long enough to grow to that size.
The lips of boas and pythons are the most sensitive heat-detectors in nature. They can sense temperature differences of a 1000th of a degree between an object and its background and judge its direction and distance with similar accuracy. Such snakes find and kill their prey in total darkness by sensing their body heat alone. The heat-detectors of rattlesnakes and pit vipers are so acute that a deaf, blind snake that has had its tongue cut off can still accurately strike its prey. Many snakes can taste air and see heat.
There is no such thing as a vegetarian snake. Snakes eat nothing except other animals. Anacondas and pythons can open their mouths wide enough to swallow deer and goats whole and a python is easily a match for a leopard or a crocodile. Whether they get indigestion is not known, but the powerful acids in their stomach mean a snake will explode if given Alka Seltzer. Most snakes eat once a week; some only eight or ten times a year. After a big meal, a python can go for a whole year without eating and female adders don’t eat for eighteen months.
WHEN DINNER’S BIGGER THAN YOUR HEAD
Keen sunbathers, snakes, like many other animals that strike fear into people, do not like to be disturbed. When this happens, most of them wriggle away. The Sonoran coral snake (Micruroides euryxanthus ‘yellow-banded small-tail’) accompanies this with small, regular, high-pitched farts. Grass snakes (which are otherwise harmless) emit a disgusting stench of rotten garlic from their anal glands. They then vomit the contents of their stomachs all over the path. If that doesn’t put you off, they flip over on to their backs and lie motionless with their mouths open and their tongues lolling out. Whether this is a defence mechanism or just bad acting is unknown. Most researchers never get close enough to ask them.
Spider
Worldwide webmaster
If spiders didn’t exist, we’d have to invent them; without them, we’d simply drown in insects. Until the late eighteenth century, we just assumed they were wingless insects, but they now have their own class, Arachnida, which contains 40,000 identified species, with as many again waiting to be named. They were one of the earliest land animals to evolve and are predatory, territorial carnivores: put 10,000 spiders in a sealed room and you will eventually end up with a single fat spider. The mass of insects eaten by British spiders in a year outweighs the UK’s human population. And by ‘eat’ we really mean drink: they dissolve their victims first.
The tarantula’s bite was supposed to bring on extraordinary symptoms: stupor, involuntary erections and an uncontrollable desire to dance off the venom in a violent and energetic dance (the ‘Tarantella’) for over three days. It turns out it was another spider’s bite that brought on these symptoms.
That’s an impressive trick, but not unique to spiders. What spiders do best is spin webs. Spider’s silk is five times stronger than steel and thirty times more stretchy than nylon. It is so light that a strand long enough to circle the world would weigh the same as a bar of soap. It is made from protein strands and water spun together; the protein gives it strength, and the surface tension of the water lends it elasticity – but we still don’t really understand how it’s done. An average spider will spin more than 4 miles of silk in a lifetime, and this can be collected and woven into garments. However, their predatory nature makes them tricky to farm, so we will have to wait for genetic engineering to deliver spider-silk parachutes, bullet-proof vests and artificial tendons.
Some spiders use their webs to fly. Called ‘ballooning’, it involves them climbing to the top of a fence, pointing their backsides into the air, squirting out a long line of silk and letting the breeze take them. They can travel immense distances and have been found as high as 16,000 feet. Spiders can create perfect webs almost anywhere, even in zero-gravity, but give them drugs and they lose the plot. In 1995, a NASA experiment revealed that marijuana made them lose concentration halfway through spinning, whereas amphetamines made them spin quicker but much less accurately. Caffeine was the most extreme: the coffee web consisted of a few threads randomly strung together.
Male spiders don’t have a penis. To mate they ooze drops of sperm on to a special sperm web. They then suck this up into one of a pair of specially adapted legs, called ‘pedipalps’. The pedipalps insert, twist and lock it into the corresponding female slots and pump in the sperm, rather like R2D2 uploading into a mainframe. Often the end snaps off on completion. Inserting these pedipalps can be a perilous business for the male: his partner can be a hundred times his size. In one species, the Tent cobweb weaver (Tidarren sysiphoides), the male chews off one of his pedipalps beforehand to gain a speed and mobility advantage over the other suitors. He usually dies on the job, his dead body keeping his sperm safe from competitors for several hours. The male Australian redbacks (Lactrodectus hasselti) actually compete to be eaten. Being devoured by the female ensures that their pedipalp gets in first.
Although spiders are surrounded by fear and superstition, humans do sometimes eat them. The Piaroa people of Venezuela consider the world’s largest spider, the Goliath bird-eating tarantula (Theraphosa leblondi), a delicacy. Roasted, they yield a quarter-pound of prawn-like white meat and are served with their fangs on the side, as toothpicks.
Starfish
No brain, clever feet
Starfish aren’t fish; they are much older. The echinoderms (‘spiny skins’), which also include sea urchins and sea cucumbers, first appeared in the early Cambrian period, about 550 million years ago, and haven’t changed much since. Unlike molluscs and insects, they have an internal skeleton made from plates of calcium carbonate called ossicles. This makes them the direct relative of all vertebrates, including humans.
They don’t have a central brain, but being star-shaped, they don’t have a ‘front’ or ‘back’ either. The nearest they get is a ring of nerves that runs round their mouth. From this an individual nerve runs down each leg. As one leg moves – usually the one closest to food – it lets the others know to follow it. A splendid advantage to this system is that starfish can regenerate
lost limbs, and in the case of the Linckia species, the lost limbs can even regenerate a new starfish. The early stages of this process – one large arm, a tiny body and four tiny arms – look like small seaborne comets.
Starfish have a mouth (underneath) and an anus (on top) but they arrived a long time before ears, eyes or noses. Instead, they have hundreds of multi-tasking tube-feet covering their underside. They use these to breathe, to move and to attach themselves to prey. They also function as noses, assisted by the skin’s sensory cells (2.6 million per square inch), responding to chemical changes in the water around them, and locking on to ‘odour plumes’ given off by potential food. At the tips of the legs, ‘eyespots’ (which may be mutated feet) act as light sensors.
In business jargon, a ‘starfish’ organisation is completely decentralised. On the other hand, passive sexual partners are sometimes described as starfish because they ‘just lie there’.