by Ted Dewan
HANDSIGHT
Raccoon droppings are crumbly, tubular and flat-ended. DO NOT EAT THEM. DO NOT EVEN TOUCH THEM. They may contain up to 250,000 eggs of Baylisascaris procyonis, a nematode worm that can cause severe illness in humans. If you eat the eggs, the larvae can migrate to other tissues, including the brain and eyes. There is no effective therapy. Raccoons look cute but many of them also carry rabies (of which they show no sign). They have bones in their penises (which people in Texas like to carry around for good luck). Dante Gabriel Rossetti, the Pre-Raphaelite poet, kept a raccoon in his Chelsea menagerie. It inspired no poetry, but did manage to disgrace itself by opening and eating its way through a whole drawerful of his manuscripts.
Rat
Man’s new best friend
Outside the polar ice-caps, the only place in the world where you won’t find any brown rats (Rattus norvegicus) is the province of Alberta in Canada. From its home base in Mongolia, the brown rat followed the spread of human cities across the steppes, finally swimming the Volga into western Europe in 1727. From there it travelled the world on ships, scurrying ashore at every port and eventually reaching Alberta’s eastern border in 1942. The Albertans decided to fight and set up a 400-mile-long buffer zone that is still patrolled by rat vigilantes. Alberta is cold and human habitation is sparse, so they may just hang on. For the rest of us, the battle was lost before it began. In the USA there are an estimated 150 million brown rats; in the UK, they now outnumber people.
Some people say that you are never more than 6 feet away from a rat but actually I believe the distance is more likely to be about 70 feet. TONY STEPHENS, Rentokil
Here’s the problem. A rat can swim for seventy-two hours non-stop. It can jump down 50 feet without injury. It can squeeze through a half-inch gap, leap 3 feet, climb vertical surfaces and walk along ropes. It can survive longer than a camel without water. It will eat anything that’s edible and lots of thing that aren’t (lead sheeting, soft concrete, brick, wood and aluminium). It reaches sexual maturity at three months. Rats have sex up to twenty times a day, and are extremely promiscuous: an on-heat female can have sex over 500 times with a barnload of different males and produce twelve litters of twenty-two young each year. In short, rats are very, very hard to get rid of.
Which would be fine if we could just grow to love them. That’s the next problem. Brown rats consume about a fifth of the food produced in the world each year. They carry over seventy extremely infectious and unpleasant diseases: bubonic plague, of course, which has killed a billion, but also cholera, typhus, tuberculosis, Weil’s disease, salmonella, crypto-sporidiosis, E. coli, foot-and-mouth, SARS and eight species of parasitic worm. A quarter of all electrical cable faults are due to rats’ ever-growing teeth, as are most ‘unexplained’ domestic fires. Like mice, their communication system involves near-constant urination – rats piss on one another to show affection, attraction, dominance and submission, and on food just to show it’s edible. Oh, and they carry a lively subculture of fleas, mites and lice everywhere they go, which is everywhere we go. It is very, very hard to love the brown rat.
Not that there isn’t plenty to admire. They are intelligent and resourceful, they learn fast and have excellent memories. Their sense of smell is of such sensitivity and refinement that it makes you wonder why they waste it all on water sports. They seem to have a sense of fun and an ultrasound giggle which they use when being tickled, during sex or when a rat they fancy sprays on them. They make very good pets, and despite the evidence to the contrary, spend almost half their lives keeping themselves clean.
FIRST CATCH YOUR RAT…
But it doesn’t matter what black pepper, salt-roasted we think. Thanks to our rat and rat kebab wasteful habits, rats are unbeatable evolutionary winners. Maybe in time the brown rat will itself be driven out, as it drove out the black rat (Rattus rattus), which in the UK at least could now apply for endangered species status. But whatever takes its place, you can rest assured that it will only be a bigger, better, smarter rat.
Salamander
How to grow new eyes
The 500 species of amphibious salamanders come in every shape and size, from the giant Chinese (Andrias davidianus) which can be 6 feet long and weigh 5 stones, to the tiny Thorius, which is the smallest land-living vertebrate at half an inch long, and the smallest animal of any kind with proper eyes.
The axolotl (Ambystoma mexicanum) is the most celebrated. Only found in a single lake in Mexico, at a certain point in their evolution they just stopped developing into adults, and now spend almost their whole life in the water as large tadpoles. Why they took this backward step isn’t clear. It might have been provoked by the land habitat around their lake becoming more hostile, but it doesn’t seem to bother other salamander species that live there. Occasionally, they do grow up into something resembling an adult tiger salamander and this can be artificially stimulated by injecting them with hormones. 99 per cent of the world’s axolotls are now kept in captivity, most of them descended from the six specimens that arrived in French zoologist, Auguste
THE MOST POWERFUL MUSCLE IN THE WORLD
Duméril’s Parisian lab in 1863.
‘Axolotl’ is the Aztec word for ‘water dog’. The builders of the original Mexico cities were paid in axolotls: they were useful as food and medicine. In Japan they are popular pets, sold as WuperRupers.
Salamanders are committed homebodies, travelling less than a mile from their birthplace over the course of their lives. This can prove fatal when the temperature changes: huge numbers perish each winter.
One species has beaten this problem. The Siberian salamander (Hynobias keyserlingii) can survive in temperatures as low as –50?C by producing antifreeze chemicals before it hibernates. They can stay frozen for many years – some may even have been slumbering since the last ice age ended, 10,000 years ago.
The most persistent myth about salamanders is that they live in fire and can douse flames with secretions from their skin (asbestos was originally called ‘salamander wool’). No one knows where or why this idea arose, but they do have a dangerous habit of sleeping in damp woodpiles …
Newts are salamanders that return to the water to breed. They are the only vertebrates that can regenerate large parts of themselves, growing new limbs, spinal cords, hearts, jaws, tails and even new lenses and irises for their eyes.
Newt cells can restart the growth process. As the damaged part heals, the cells reverse their original function and turn back into an undifferentiated lump called a blastema (from the Greek blastos, bud) from which the replacement limb or tissue grows. If a blastema is moved to another part of the salamander’s anatomy, the missing bit will start growing there.
How the cells know what to grow isn’t understood, but salamanders are being studied closely to see whether human tissue could be stimulated to regenerate. Also, because malignant tumours seem to grow in a very similar way – injecting cancerous tissue into newts can also cause a new limb to grow – they may hold important clues in the fight against cancer.
Scorpion
Fluorescent assassin
Scorpions were the first predators to crawl out of the sea on to the land, and they have evolved very little in the last 430 million years because they are very good at what they do. In their prime, during the oxygen-rich atmosphere of the Carboniferous period, scorpions as big as dogs roamed the land, and in the sea giant water scorpions grew to twice that size. Like their younger arachnid cousins, the spiders, scorpions are tough and adaptable, putting up with sub-zero temperatures and desert heat. They can even survive two days completely submerged in water. They are found on all major land masses except Greenland and Antarctica. For 200 years, an illegal immigrant colony of yellow-tailed scorpions (Euscorpius flavicaudis) has lived in the harbour wall at Sheerness in Kent.
Isidore of Seville believed that scorpions were formed from the dead bodies of crabs and, though very fond of the smell of basil, will never sting the palm of your hand.
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bsp; Part of this indestructibility is due to their highly efficient metabolism. They eat slowly but for several hours at a time, dissolving their prey with powerful stomach juices, and leaving behind a small ball of indigestible tissue. A single meal can increase their weight by a third, and some species can survive on that for a year, storing their food as glucose in a large liver-like organ. They burn energy at a quarter of the speed of insects and spiders and very few scorpions ever need to drink. This gives them an advantage as predators but they are also very well equipped when they do need to kill. They have two sets of eyes: one to tell them the time of day or night and a more complex set, with lenses and retinas, that are the most light-sensitive organs of any invertebrate. Using the hairs on their claws they can triangulate the precise position of lunch, picking up vibrations caused by movements as slight as 25 millionths of an inch.
Unusually for an arthropod, a female scorpion gives birth to live young. Even more extraordinarily, some species are pregnant for longer than humans. They are one of the very few invertebrates to have independently evolved a womb where embryos are fed by teats linked to the mother (rather than by the yolk of an egg). Labour can take days, with up to a hundred offspring scurrying up their mother’s claws to nestle on her back underneath her sting, so nothing can get to them. Nothing that is except the mother, who, if suddenly peckish, may snack on them herself.
Despite the widespread myth, scorpions do not go mad and sting themselves to death when a drop of alcohol is placed on them, or when confronted with fire, as they are immune to their own venom. Of the 1,500 known species of scorpion, only twenty-five have stings that are dangerous to humans; most are no worse than a bee sting. Scorpion venom can even save lives: protein from the Israeli yellow scorpion’s (Leiurus quinquestriatus) venom has been used to kill brain tumours.
Scorpions are fluorescent under ultraviolet light as a result of special proteins in their exoskeletons. As they can’t see this themselves, no one is quite sure why. It might be to mimic insect-attracting plants, to warn off predators or even to act as an in-built sunscreen.
DIRTY DANCING: SCORPION ‘FOREPLAY’
Sea Cow
Slow and seductive
The sea cow family, or sirenians, contains the dugong (Dugong dugon) and three species of manatee (Trichechus, after their ‘hairy’ snouts). As their common name suggests, these large, docile creatures are the only aquatic mammals that live on plants. Although they look like grey tuskless walruses, their closest relatives aren’t cows, walruses or whales but another large herbivore, the elephant.
Manatees often congregate near power plants, because of the warm water. In return, they keep the surrounding channels clear of weeds.
Sea cows have a very laid-back life. They paddle around in warm tropical seas, with little competition for food and no natural predators. As a result, they have a very leisurely metabolism. The largest adults weigh over a ton and spend eight hours a day slowly chomping through six straw bales’ worth of aquatic plants, which take a week or more to digest. Life is slow enough for algae and barnacles to grow on their skin. Some dugongs have been recorded as living into their seventies, and they only manage one calf every three to seven years.
When they aren’t eating or sleeping, sea cows come together regularly to ‘cavort’. These sessions of nuzzling, bumping, kissing and mutual masturbation are often male-on-male, but can involve up to four individuals of either sex and last for several hours. The normally silent manatees make a sequence of distinctive ‘snort-chirps’ as they cavort, though no one knows how (even if we can guess at why). This pleasure-filled life, combined with the female dugong’s large and elaborate clitoris and pendulous ‘breasts’, has contributed significantly to the mermaid myth. In the Solomon Islands, ‘dugong’ is the slang term for prostitute.
Dugongs and manatees also have a reputation for stupidity and their brains are, proportionally, small and smooth, roughly the equivalent of our brains shrunk to the size of a plum. In their defence, their brains seem well up to the job and some have even been trained to recognise colours and patterns in return for food.
More significantly, low metabolism and the absence of stress help make them impervious to the diseases which afflict other mammals, propelling them to the forefront of research into cancer and HIV.
This may also explain why they have six neck vertebrae rather than seven. In mammals, the genes that specify the number of vertebrae also control the nervous system and cell growth. Changes in this genetic data can cause cancer, so natural selection has tended to leave them alone. However, in a low-metabolism mammal like a sea cow the risk of cancer is greatly reduced. Over time, this might have allowed the genes to risk variation. Interestingly, the only other mammal with an irregular number of neck vertebrae is the sloth, another noted slacker.
‘Manatee’ comes via Spanish from a Carib word meaning ‘breast’, while ‘dugong’ derives from Malay ‘duyung’ meaning ‘lady of the sea’. Like elephants, they have two teats under their forelimbs, causing sailors to mistake them for mermaids.
But there is a downside. Slow, inquisitive and delicious (roast dugong tastes like veal) is a bad combination when faced with Homo sapiens. All four sea cow species are now endangered, as result of hunting, pollution and damage from propellers and fishing nets. The historical precedent is grim. Their relative, the Steller’s Sea Cow, three times the size of the largest manatee, was hunted to extinction in the twenty-seven years after its discovery in 1741.
Sea Cucumber
Streetsweeper of the deep
Sea cucumbers have been trundling along the bottom of all the planet’s oceans for 500 million years. They do an essential job as marine binmen, processing over 90 per cent of all the dead plant and animal material that settles on the sea floor. Many of them do look like knobbly cucumbers. Their family name, Holothuridae, is thought by some to mean ‘completely disgusting’. The Romans called them phallus marinus, presumably because of their shape, and even Darwin dismissed them as ‘slimy and disgusting’. One Mexican species, Holothuria mexicana, is known as the Donkey dung: a perfectly accurate, if unflattering, description.
THE INNER CUKE
Despite their shape, the 1,100 species of sea cucumber are close relatives of the starfish and the sea urchin, sharing the same fivefold body symmetry and, like them, moving on tube feet driven by piped seawater. But ‘cukes’, as marine biologists call them, have other tricks. They breathe through their bottoms, drawing in water through their anus to fill a respiratory ‘tree’ and then expelling it along with any digestive waste that might be lurking. Single hole: two functions. This fact has been exploited by the tiny eel-like pearlfish. They wait until the cucumber’s anus opens in the morning and then sneak inside, spending a leisurely day swimming around the intestines, before emerging again to feed at night. Some even knock to gain entry. Juvenile pearlfish are less welcome as they have a habit of gnawing on the cucumber’s gonads.
Sea cucumber was Australia’s first food export. Aborigines on the northern coast traded them with Indonesian fisherman from as early as the sixteenth century.
Cukes are nocturnal and need to fill sixteenth century. their guts at least twice a night, so life mostly alternates between sand-vacuuming and resting. If they are stressed or threatened, they have an impressive array of escape strategies. Their bodies are made from a connective tissue called ‘catch collagen’, which gives them an almost miraculous ability to change from solid to fluid. This enables them to ‘pour’ into the tiniest crevices and then stiffen again so they can’t be extracted. Some species can blow themselves up to the size of a football. Others expel water to make themselves look like pebbles, but the ultimate cucumber party-trick is to blow their guts out of their bottom and flood the surrounding water with a toxic soup. Known as a ‘cuke nuke’, this can wipe out all the fish in a small aquarium, as well as the cucumber itself.
Some species have a more sophisticated version, expelling fine sticky threads, known as Cuvierian
tubules, out of their backsides. These form an astonishingly sticky net which can tie up a hungry crab for hours. On the Pacific island of Palau, islanders milk cucumbers of their tubules and bind their feet with them to make improvised reef shoes. They are also used as a sterile dressing for wounds. Amazingly, a cucumber that has been harvested of its guts, gonads or tubules can grow them back within a couple of months.
Dried sea cucumber, known as trepang or bêche-de-mer, is eaten as a delicacy all over Asia, and has a reputation as both an aphrodisiac and a painkiller. The global sea cucumber market has grown to £2.3 billion and this is putting pressure on some species, leading to the establishment of cucumber farms and sea ‘ranches’.
Seal
The grizzly submarine
Don’t be fooled by their cute looks: the seals’ closest relatives are bears and they can be every bit as vicious. One of the ways you can tell if a Leopard seal (Hydrurga leptonyx) is in the area is an empty penguin skin floating on the water. They violently shake the hapless bird from side to side to remove its coat and then gulp down the naked corpse. They are almost as bad with their loved ones. The male Southern elephant seal (Mirounga leonina), six times larger than his partner, occasionally gets carried away during copulation and accidentally crushes her skull between his massive jaws. And when female Hawaiian monk seals (Monachus schauinslandi) come into heat they risk being ‘mobbed’, which is the polite scientific term for being battered to death by a gang of amorous males. In order to save the species from extinction, males are now being put on libido-suppressing drugs.