by Simon Barnes
Aardvarks are so good at termites and ants that their numbers are diminishing – but not because they are killing and eating all the termites. The problem is that they are so good at what they do that they have no room to be good at anything else. They have driven up an evolutionary cul de sac: and that’s all fine and dandy so long as everything around them stayes the same. Hyenas, jackals, vultures, storks, geese, pangolins, bat-eared foxes and aardwolves all eat termites, but not half as well as aardvarks. But all these others take other food as well, while aardvarks don’t. The very strength of the aardvarks has made them vulnerable. The extreme specialist cannot adapt to changing circumstances. This is a conundrum sometimes called the tender trap. Intensive arable farming reduces the number of termites and therefore the number of aardvarks. The aardvarks, who appear so early in the dictionary, are creatures with no Plan B.
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I. Quotation from The New Encyclopaedia of Mammals, edited by David Macdonald.
Unkillable bears
I must confess I had an Unworthy Thought in the course of putting this book together. Temptation shook me as a terrier shakes a rat, as it says in one of the great Modesty Blaise thrillers.I I thought it might be a smart wheeze to stick in a couple of hoax chapters.II
I could, for example, devote a chapter to something gloriously unlikely but borderline plausible, like flying mice. And I reckoned people would swallow just about anything when it came to inverts, so I could describe, say, a miniature bear with eight legs that you can boil or freeze or smother with radiation and still not kill it. But on second thoughts, I realised that nobody would believe that sort of thing.
If the principal aim of a living creature is survival,III we are wasting our time being human. If we want to lead the world in the art of survival, we should have been water bears. These tiny creatures are the all-Animalia masters of survival. For a start, you can find them everywhere in the world. They can cope with the tropics, and they can cope with the Arctic and the Antarctic. They are microscopic. Most species are less than a millimetre in length. They have four pairs of stubby legs, and they were named by their discoverer, Johann August Ephraim Goeze, who thought that their rolling, shambling gait was rather bear-like. So he said each one was ein kleiner Wasserbär, a little water bear, and they make up their own phylum with around 1,000 species. This is the phylum of tardigrades, or slow-steppers. They are sometimes called moss piglets.
That’s because the easiest place to encounter them is on a chunk of moss. They prowl these miniature forests in their ursine amble, armed with jaws than can pierce cell walls. They use them to suck the life out of moss and algae, occasionally out of tiny invertebrates. And this frankly uncomplicated way of looking at the world has made them brilliantly ubiquitous. They have been found at 6,000 m, 20,000 feet, in the Himalayas; they have been found a depth of 4,000 m, 13,000 feet, in the ocean. They have been found under 5 m, 16 feet, of ice. In a single litre of sediment, freshwater or marine, you can find 25,000 water bears.
They can survive almost anything. They have failed to die at temperatures close to absolute zero. Boiling is nothing to them: they have survived temperatures of 151 degrees Celcius. They can stand 1,000 times more radiation than humans. They have been sent out into a low earth orbit and come back safe and sound. And when things get absolutely impossible, they have one more trick up their microscopic sleeve. They can just shut down and wait for things to get better. They can do this for ten years. When there is no moisture, they go into a phase called cryptobiosis: hidden life. It has been described as the instant coffee phase: they become flecks – almost completely nothing – and yet when a droplet of water comes along, they become living things once more. Some species have avoided that messy sex stuff, and have gone in for virgin birth, for parthenogenesis: an exclusively female population laying viable eggs. Just about everything they do is remarkable. Or perhaps it isn’t, because what they do is survive.
This chapter full of fantastic achievements reminds me of the werewolf’s boast in The Chronicles of Narnia:IV “I can fast a hundred years and not die. I can lie a hundred nights on the ice and not freeze. I can drink a river of blood and not burst. Show me your enemies.” This speech is about deep and frightening magic, the sort of thing that confounds the reader’s expectation of what is possible and what is not. But down there, under the wrong end of the microscope, the water bears are doing the same sort of thing as a matter of routine.
I could, I suppose, put in a werewolf chapter in this book and try and make you believe it, though I don’t suppose I’d succeed. But here we have an entire phylum of creatures, creatures found all over the world, at either end, in the middle, on the roof and in the cellarage, and they perform the werewolf’s miracles as part of their daily lives. There really is no point in making up stuff about the wild world. The wild world is better at invention than we are: it not only has an infinitely deeper imagination, it has been doing it for millions and millions of years.
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I. From The Impossible Virgin by Peter O’Donnell, one of the 11 novels and two collections of short stories devoted to Modesty Blaise.
II. This is not a double-bluff, I promise you.
III. This may look at a cursory glance like a reference to Richard Dawkins. It is nothing of the kind: Dawkins’s contention is that the survival of the gene is what counts, that the host body – that’s you, me, the aardvark and the water bear – are just survival machines for our immortal genes. This, in fact, is basic scientific orthodoxy, but Dawkins expresses it in particularly uncompromising terms.
IV. From Prince Caspian, in the chapter called “Sorcery and Sudden Vengeance”.
Flying flashers
I have no option, then, but to write about flying mice. Admittedly they’re not mice and they can’t fly, but apart from that the description is exact. But they look an awful lot like mice, and while they can’t fly, they can most certainly glide. They operate on the same principle as the better-known flying squirrels, which make up a quite different and unrelated group. There are two species of flying mice, the long-eared flying mouse, and the confusingly named pygmy scaly-tailed flying squirrel. They are among seven species in the family of Anomaluridae, of which only six can get airborne. The two flying mice species form the genus Idiurus.
The flying mice glide by means of a membrane between their front and back legs which they open out – rather in the manner of a flasher – when they take to the air. They are from the vast and various order of rodents. They are a bit bigger than the house mouse that most of us have encountered, however reluctantly, about twice the size in fact, measuring up to 4 inches, 10 cm, without the tail, and weighing up to 1.2 ounces, 35 grams. They have a long tail that doesn’t have much hair on it, but it has raised scales and patches of scaly skin to grip branches. This is interspersed with long hairs, which make the tail rather feather-like when used in aerial action and stretched out for balance. They are found in West and Central African forests, and they are nocturnal. Not a lot is known about them, because they are hard to find and almost impossible to observe.
Gerald Durrell managed to catch some by smoking them out of their homes in hollow trees, though his attempt at keeping them in captivity was, alas, a failure. The reason I know about flying mice – they don’t make it on the nature documentaries, and they are seldom found in pictorial reference books – is because of his description.I “I have seen some extraordinary sights at one time and another, but the flight of the flying mice I shall remember until my dying day. The great tree was bound round with shifting columns of grey smoke that turned to the most ethereal blue where the great bars of sunlight stabbed through it. Into this the Idiurus launched themselves. They left the trunk of the tree without any apparent effort at jumping; one minute they were clinging spread-eagled to the bark, the next they were in the air. Their tiny legs were stretched out, and the membranes along their sides were taut. They swooped and drifted through the tumbling clouds of smoke with all the assurance an
d skill of hawking swallows, twisting and banking with incredible skill and apparently little or no movement of the body. This was pure gliding, and what they achieved was astonishing. I saw one leave the trunk of the tree at a height of about thirty feet. He glided across the dell in a straight and steady swoop, and landed on a tree about a hundred and fifty feet away, losing little, if any, height in the process. Others left the trunk of the smoke-enveloped tree and glided round it in a series of diminishing spirals, to land on a portion of the trunk lower down. Some patrolled the tree in a series of S-shaped patterns, doubling back on their tracks with great smoothness and efficiency. Their wonderful ability in the air amazed me, for there was no breeze in the forest to set up the air currents I should have thought essential for such intricate manoeuvring.”
It is clear that the ability to cross the gaps between trees is a huge advantage for those that possess it. That’s clear from the fact that this ability has evolved independently four times over in mammals alone. We have the flying mice and the rest of the Anomaluridae. There are 44 species of flying squirrels. There are two species of colugos, also called flying lemurs, though they are not actually lemurs at all – common names are often confusing and approximate (we have already established that a jellyfish is not a fish). There are also marsupial gliders found in Australia and New Guinea, the flying phalangers. These four groups do not share a close common ancestor: each arrived at the same solution by a different route: another striking example of convergent evolution. Lizards, frogs and even snakes have also evolved, and again quite separately, the ability and equipment for gliding.
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I. In The Bafut Beagles Durrell, at his best, is one of the finest nature writers ever to have picked up a pen, and by a distance the funniest. His My Family and Other Animals has rightly become a classic, but there are more than 20 more, not counting his fiction, and they’re all full of good things. This chunk is quoted with the kind permission of Lee Durrell. The Durrell Wildlife Conservation Trust and the Durrell Wildlife Park on Jersey still carry on the work of this pioneer conservationist.
Cans and cans of worms
A fellow sports journalist told me a story about his days on local papers. He had been covering the local non-league football club, just as I used to do myself. Most non-league clubs are small places in which everybody knows everybody else and we all go into the bar for a drink afterwards. After one match, one of the players left his group of team-mates to approach the journalist. He stuck a thick index finger under his nose. “If you ever call me again what you called me in the paper this week, I’ll beat the crap out of you.” The journalist was mystified, because he remembered that the player had had a pretty decent game and that he had made of point of saying so in his match report. When he got back home he checked out what he had written. The offending word was “ubiquitous”.
You don’t get much more ubiquitous than a nematode worm. Practically every living animal on earth is a nematode worm. It has been estimated that 80 per cent of the animals alive right now are nematodes. You can find a million individuals in a cubic metre of soil. Nothing teems like nematodes. They are sometimes called roundworms, and they have a phylum to themselves, Nematoda. So far 28,000 species of nematodes have been described, of which 16,000 are parasites. Most of them are tiny: around 2.5 mm, 0.1 inches, in length is typical, though there are some free-living giants of 5 cm, 2 inches, and some of the parasitic ones are longer still.
They are called roundworms for the excellent reason that unlike flatworms, they are round. The roundness gives them a muscle-lined body cavity, and so, unlike flatworms, they have a digestive system with a mouth and an anus. The cylindrical body is covered in a cuticle, which they moult every so often. They have what is described as a “relatively distinct head”. Heads are by no means essential in life, even animal life, as we have seen with corals and jellyfish. There’s no point in being headist.
Nematode worms lack the unkillable qualities of the water bears, but they are the world champions when it comes to ubiquity. You really can find them anywhere. Fresh water, salt water, ocean trenches, mountains, deserts, every continent. It is reckoned that 90 per cent of all life forms on the ocean floor are nematodes. They have been found far beneath the earth: even 3.6 km deep in a South African gold mine. They can survive heat, drought and frost, and many are capable of shutting down, enclosing themselves in a cyst. When things go well they can capitalise with extraordinary speed: a single individual can lay hundreds of thousands of eggs in a day.
They parasitise many species of plants and animals, including humans. The dreadful Loa loa worm, Sir David Attenborough’s argument against a sweet-natured creator, is a nematode. Hookworms, pinworms and whipworms are among those that infect humans. It has been estimated that a quarter of all humans on earth are infected by nematodes: a condition associated with a warm climate, poverty, poor sanitation and overcrowding. The commonest form is ascariasis; a few people in Britain are diagnosed each year, though it is always something brought in from warmer places. The infestation may not have any symptoms at all, but in more severe cases you find fever, vomiting and diarrhoea. Infection is generally caused by (sorry to bring this up again) faecal contamination of food.
Pets and other domestic animals are often “wormed” to get rid of nematodes. But the forces of evolution can create some bizarre and ingenious methods of survival. There is a species of nematode that parasitises the fig wasp, which is the only pollinator of figs. There is another that infests a species of tropical ant. The condition causes the ant to develop a bright red gaster – which is what we scientists call the back end. Infected ants are more sluggish and carry the gaster in a bizarre way. This singles them out, and they get eaten by birds who mistake them for berries. The worms are excreted by the bird and when all goes well, the droppings are gathered in by the same species of ant, in order to feed the larvae – and that keeps the cycle spinning along very nicely, at least for the worm.
Some nematodes parasitise plants and affect the yield of commercial crops. The root-knot nematode is a particularly damaging species. Here you have a dilemma: they can be killed all right, but only at the expense of all the other species of nematodes. And many of them are beneficial. You can buy nematode worms from garden specialists and set them out in your garden to control slugs and other unwanted animals.
Self-sharpening chisels
Every idea is a great idea if it allows you to make a living on this tough ol’ planet. That is true for animals, for plants, for fungi and for the five (or so) other kingdoms, all of differing kinds of microscopic life. Quite often, the forces of evolution come up with a design that works so well that it can be used for more than one species. Every now and then, you find a concept that works for quite a large number of species. The combination of large brain relative to body size, grasping hands with opposable thumbs and stereoscopic vision works well for us primates, and as we have seen, there are about 300 of us when it comes to species.
Which makes primate design a pretty good idea, but not half as good as self-sharpening teeth. That is the stroke of genius that allowed rodents to radiate out into 33 families containing more than 2,000 species. One authority states categorically that there are 2,277 species of rodents, but as we know, these things are in a perpetual flux. Still, flux or no flux, that’s an awful lot of species to hang from one basic design coup: more than 40 per cent of all mammal species are rodents. Naturally, it is the teeth that define their difference from the rest of us.
When we think of rodents we tend to think of teeth. Timothy Spall played Wormtail in the Harry Potter films, a character who spends 12 years as a rat. When he resumes human form, his prominent teeth make him look as if the transformation were only 98 per cent complete. Laurence Olivier played Shylock in The Merchant of Venice with false teeth designed to give him an appropriately rat-like face. All real rodents live and die by their teeth. Their unique arrangement is in the incisors: the ones at the front, two pairs, one top and one bot
tom. Often orange or yellow. These teeth grow throughout their lives. The front-facing surfaces are conventionally enamelled; the back surfaces are not: they are exposed dentine. The teeth close over each other, and this creates a self-sharpening mechanism which means that the enamel edge is honed every time the animal closes its mouth. As a result, the edges are always as sharp as chisels.
Rodents gnaw. If they stopped gnawing their teeth would grow out of control. Small rodents gnaw small stuff, on the whole, while big rodents gnaw big stuff. Beavers gnaw down entire trees and change their local environment as they do so. This gnawing ability gives rodents a great advantage: they can eat seeds in hard cases, food unavailable to less well-endowed animals. They can gnaw through all kinds of things to reach food. They also use their teeth in self-defence if they have been unable to pre-empt confrontation by running away. The image of the cornered rat is one based on fact; all predators prefer easy prey, because they are not in it for the sport. An animal that makes itself painful to kill is giving itself a considerable advantage over a mere fleer. Rodents also have a clever device to stop them choking to death on wood splinter or seed husks: they can suck their cheeks into the gap between their self-defining incisors and the comparatively mundane cheek teeth set further back in the jaw.
