by Simon Barnes
BarnaclesIV have shells, like oysters and snails and cockles and mussels, so it seems obvious that they’re all one and the same. But barnacles aren’t molluscs: they are crustaceans, and so they belong in the phylum of arthropods. It’s yet another of the counter-intuitive truths of the wild world: barnacles and limpets lie adjacent on the same exposed rock in the intertidal zone and seem to be living much the same sort of life. But they came at it from different evolutionary directions. Barnacles are more closely related to the butterfly that strays across the beach than to the limpets that squat alongside them.
Barnacles are technically cirripeds, or curly-feet. There are about 1,220 species, and in their adult, static form they lie on their backs and extend their curly feet into the water above them and waft food particles down to be consumed. They are mostly to be found in shallow water and the areas between the tides, though some species are parasitic and live inside crabs. They go through two distinct larval phases, and that separates them from molluscs and allies them with arthropods.
This minute study of small but crucial differences in closely related species reveals without compromise the tendency of evolution to create radiations of species. Darwin perceived in delight how aspects of barnacles were analogous to the head of a crab but “wonderfully modified”. Here is evolution in action: here is a clear example of the mutability of species. He observed further than the organ that worked as the oviduct – egg-laying implement – of a crab had become “modified and glandular and secretes a cement”. The cement is used by the larva to attach itself to a rock and become static, or sessile, as scientists prefer to say. In other words an organ can change its function from one related species to another: a crucial truth about evolution.
Eventually, after those eight unending years, the damn thing was done. Thus the brilliant amateur was now recognised by all as a solid professional: a man who had done the hard yards. Thomas Huxley was to call the barnacle monograph “one of the most beautiful and complete anatomical and zoological monographs which has appeared in our time”. By the end, though, Darwin wrote: “I hate a Barnacle as no man ever did before, not even a sailor in a slow-moving ship.”V It was time to move on.
Counter-factual history: Darwin decided against barnacles because it was too much like hard work, especially for a sick man.VI He put together his big work without it: and it created no stir whatsoever. No one took it seriously. It was just some half-baked notion of a gentleman adventurer who thought a wealthy background and a best-seller were enough to make him a scientist. Darwin’s name was forgotten. So: did the truth remain hidden for many years? Or did Alfred Russel Wallace persuade science that his own understanding of evolution by means of natural selection was valid? Would Wallace have written as convincingly, as exhaustively, on the subject as Darwin? Would he have been believed? Would this scientific and cultural breakthrough have been delayed for years had Darwin not decided to spend eight years looking at barnacles?
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I. Darwin was not the only one with a beloved barnacle in his life. In 1904 James Joyce eloped with Nora Barnacle. His father remarked: “Well, begod, she’ll stick to him.” They stayed together until Joyce died in 1941.
II. His children, visiting friends, asked: “Where does your daddy keep his barnacles?”
III. See two excellent biographies: Darwin, by Adrian Desmond and James Moore, and Charles Darwin by John Bowlby.
IV. In medieval times it was generally understood that geese hatch from barnacles; or to be more precise, that barnacle geese hatched from goose barnacles, a group which do look a little like the heads and necks of geese. This somewhat odd notion made it acceptable to eat geese at times when meat was forbidden, like Fridays and during Lent. It was not, then, a story that people were overeager to prove false.
V. Joyce also knew what it was to get fed up with a work of genius. “For seven years I’ve been working at this book – blast it,” he once wrote of Ulysses. He then spent 17 years on Finnegans Wake.
VI. It has been speculated that Darwin suffered from Chagas disease, a parasitic infection that he might have picked up in South America while doing his stuff on the Beagle, though this idea has been losing ground in recent years.
Secret snakes
The Luangwa Valley is full of birds that eat snakes. The bateleur cruises the airways of the valley looking for snakes: the western banded snake eagle and brown snake eagle are specialists which mostly look for snakes from a high perched vantage point. The lovely lilac-breasted roller takes small snakes in the same way. You wonder how they ever find enough to survive, because I’ve hardly ever seen a snake in the valley. You don’t often bump into one. Then there is the excellent A Guide to the Snakes of the Luangwa Valley, by my old friend Craig Doria, and Patrick Nyirenda. One of the spooky things about this book is that most of the sightings of snakes – and perhaps most especially the venomous ones – seem to have taken place in the camps and lodges. It’s as if you’re more likely to meet a snake while walking from your hut to the bar than you are out in the bush.
This doesn’t represent the reality. It’s just that there are more people-hours spent in camp than anywhere else in the national park. You can go looking for birds and they’re everywhere to be seen. It’s much harder to look for snakes. You are most likely to find one by chance, and the laws of chance state that you are most likely to see them in the place where you spend the most time. I remind myself of that when I take a pee in the middle of the night.
In other words, (1) snakes are more numerous than we think and (2) they are very talented at keeping out of the way of humans. Their shape gives them a different understanding of the world’s possibilities: they are good at the low and the narrow and the hidden; they are also good at climbing in silence and obscurity. Being reptiles, they are very good indeed at being still. You can walk through a landscape of snakes without knowing it. In fact, I’ve seen people doing so: with their dogs merrily bounding about as they go.
Dunwich Forest in Suffolk is a favourite dog-walk, and is much crossed and recrossed. It’s not a place where you’re ever going to be lonely for long. Those interested in cold-blooded terrestrial beasts are herpetologists, herpers for short, and I was in the forest with a crack herper called John Baker. It was the beginning of spring. We walked along the south faces of the windrows, the long piles of brash and bracken. And time and again, he would say: “Adder.” And I would ask where and he’d tell me and I still couldn’t see it. Eventually I would almost prise it out of the landscape with my eyes: the same colour as the dead bracken fronds and the same pattern, but a warmer tone. And sometimes, very subtly, in movement. He must have shown me 30 or more in a couple of hours’ walk. This is their place. They are venomous snakes, they are all over the forest, but it takes a person with the right eyes and the right educated mind to encounter one.
Few people are aware that England’s green and pleasant land is home to snakes 5 feet long, 6 six, nearly 2 m. Female grass snakes can reach this length: and they have a respectable girth, too: substantial snakes. I saw one swimming in a pond in Suffolk: a majestic lady crossing the open water with impressive lateral undulations. I found it rather wonderful to think that even in safe southern England, there are snakes the length of hosepipes laterally undulating about the place, while in the most well-trodden of woods, venomous snakes get on with their lives without troubling a soul, and with scarcely a soul aware of their abundance.
I know this won’t come as happy news to those who suffer from a fear of snakes – from ophidiophobia, to be more technical. So it serves me right that I must now move on to spiders.
The silk route
Silk is the glory of the spider. As Eskimos are (wrongly) supposed to have dozens of words for snow, spiders (genuinely) have many different forms of silk and many more different ways of using it. Building webs is just the beginning of it. I must tell you first of a thing of beauty and wonder that is all the work of spiders, something so lovely that it charms even me on a regular
basis. In my previous place, I used to start most days with a climb up what we in East Anglia call a hill: certainly a reasonable slope by the most demanding standards. It used to catch the low morning sun in the autumn as I headed up to feed the horses. And when a bright morning coincided with a hefty dewfall, the field was transformed. It became an enchanted place, a fairyland of spiders. It seemed that every two blades of grass were linked by a golden thread a few inches long: a strand of precious metal that trembled slightly when the breeze shook it. It seemed as if I was walking through not a pasture for horses but a crop of gold: a waiting gilded harvest that had sprung in delicate strands from the bosom of the earth.
The sun, shining through the dew, had called them into being: a classic epiphany that is sometimes called a gossamer morning. Each thread represents the journey of a spiderling. A hatch-out of spiderlings continues with a great adventure, a surrender to chance. Each tiny spider extrudes several strands of silk, and these catch the air on a windy day, and up and away goes that spider to land – a few yards away, or sometimes a field of two away, or sometimes for miles, at times crossing continents and oceans. No island can spring up anew from the volcanic pulse of the earth without eventually being colonised by speculative spiderlings. The trick is called ballooning, though it’s more like kiting, except that in a neat paradox, the string is used not for tethering but for flight itself. Ballooning spiders have been gathered as aerial plankton thousands of feet above the surface of the earth, and they have been found on ships in the middle of the ocean.
Spiders’ webs are beautiful and admirable things, especially when the dew or frost chooses to set off their wonder. An orb-web – a roughly circular construction – of a few inches is a delightful thing to come across in the garden. They are rather more daunting when they reach over 3 feet, a metre across the diameter. The large woodland spider of Hong Kong is a particularly impressive craftsman – craftswoman, rather: the enormous black and yellow females stand in the centre, comfortably bigger than your hand with a web that looks as if it could snare a child. My copy of A Colour Guide to Hong Kong Animals has a photograph of a large woodland spider with a pipistrelle bat caught in the strands of the web. The bat is half-eaten:I she was saving the rest for later.
Roald Dahl wrote a short story called “The Visitor”, in which the sinister and exquisite seducer Oswald Hendryks Cornelius keeps a greenhouse full of spiders; he harvests the webs every now and then and has the silk made into ties. He is the only person with the nerve to enter that dreadful place. Spider silk is remarkable stuff, and perhaps ever so slightly sinister to us humans because we can’t empathise with the idea of producing it. How can you just think something into being: something so brilliant and so strong, so multifunctional? And like the man who could blow hot and cold from the same mouth, spiders can produce up to seven different kinds of silk from the same organ. Some insects make silk, but they can only make the one kind. It is the spiders who are the masters.
They use silk for catching prey, sometimes in the form of webs, most notably the wheel-shaped orb-webs. They also make traps for prey in the shape of tubes and funnels and tunnels and tangles and domes. They make traps like lace; the bolas spider uses single strands in a kind of fishing technique. Some spiders use silk to immobilise prey, wrapping it up like a mummy. Silk can be used in reproduction, with males making a silken parcel of sperm. Silk is used for dispersal by the ballooning spiderlings, as we have seen. Webs are made of protein and can be used as food: some spiders will eat the webs of other spiders. Many spiders will eat their own webs, as part of the economy of energy. Some spiders will line a nest with silk. Some leave silk guide-lines, so they can find their way back to base with ease. Others create silken drop-lines, so that when threatened, they can just let go and plummet – and yet do so without falling into other possible dangers. Some spiders lay alarm-lines of silk that are triggered by passing prey. Some find mates by leaving a pheromone trail of silk.
It’s extraordinarily tough stuff. The combination of strength and elasticity makes it astonishingly durable. Weight for weight it’s as strong as steel alloy; the fact that it can stretch up to five times the length of its relaxed state makes it incredibly hard to break. Silk is a small lesson in the way life works: when you get a very good idea, it can be adapted and readapted again and again, in uses far removed from its original propose. If silk originally evolved for a single way of catching prey (and that’s speculation) it is now used in many different ways for that purpose – and also for life-saving, infant care, nutrition, escape, exploring the world, and love.
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I. To be more accurate, half digested. Spiders don’t munch and swallow: some inject their prey with digestive juices and then suck; others mince up their prey and then add the digestive enzymes. It’s called external digestion.
Disgusting clumsy lizards
Lizards are more or less the default reptile. Mostly, if it’s a reptile, it’s a lizard: around 5,600 species of them, penetrating all kinds of habitats from the Arctic Circle down to the tip of South America: up in the trees, on the ground, among rocks, in the water, burrowing in the earth. Unlike snakes they have firm, locked jaws and external ears. They mostly have four legs, but some of the burrowers have done away with them, like slow worms, already met in these pages. Lizards range from tiny chameleons and geckos no longer than your finger to the komodo dragon. Out in the Indonesian archipelago on an island with no large carnivores, the lizard has taken the alpha predator role and become a giant: up to 11 feet, 3.3 m, in exceptional individuals, and known on occasions to have killed humans. Most are less than 3 m or 10 feet, which is still a fair size.
Those who have lived in Southeast Asia are familiar with the house geckos shinning up the wall, operating on a private theory of gravity, pop-eyed, with translucent skins that make most of their inner organs available for inspection. They are almost invariably welcomed because they eat mosquitoes, which is an endearing trait, and have such a charming appearance, hiding behind framed pictures during the day and coming out at dusk. They utter a pleasing chuckle: in Bahasa Melayu (the Malay language) they are an onomatopoeic cheechak. Out in Africa you can find the Nile monitor, a seriously imposing lizard, which can make 1.6 m, 5 foot 3 inches, and weigh 15 kilos, 33 pounds. Like snakes they taste the air with their tongues. They swim with immense confidence.
We associate lizards mostly with hot places, scurrying out of sight in an instant of time when your shadow falls across them in the heat of the Mediterranean day. To have the same experience, though at a lower temperature, is always a surprise in Britain, but the common lizard loves a good bask on a sunny day and is more often encountered than you might expect, though it is more frequently seen in the tail of your eye than in plain view.
Lizards are not to be underestimated in their adaptability. This is a lesson that Charles Darwin almost learned in the Galapagos archipelago during his famous trip on the Beagle. The Galapagos section of his great travel book is full of look-behindjer moments. When we read the book in the 21st century, we already know about evolution, we already know about Darwin on the Beagle, we know already about Gregor Mendel and how his pioneering study of genetics showed us the mechanism by which natural selection operates. We also know that the Galapagos are full of creatures that evolved uniquely for the place: and that as a demonstration of evolution in action, can’t be bettered.
But the fascinating, almost bewildering fact is that Darwin didn’t know that. When he found a unique lizard that dived into the sea to forage for seaweed, he had no idea that he was looking at one of the extraordinary Galapagos specialities: a creature that would become a classic example of evolution in action. Museum specimens of the marine iguana had been labelled with the erroneous information that they came from the South American mainland. Sometimes when you travel, you find something odd, but you think it’s just you. You think the entire place is like that: you’re just not used to it yet. So it was with Darwin and the marine iguana: he wrote about
them as “disgusting clumsy lizards” and moved on.
But I suspect that a great deal of this bizarre stuff on the Galapagos archipelago joined the great menagerie of sleeping influences on his future thinking. I suspect that the oddness, the uniqueness, stayed with him, and was part of the furtive development of his great notion: the one that finally reached its eureka moment when he turned to the work of Malthus, and read that more humans are born than survive into adulthood to produce children of their own. Yes: and that’s true of all animals. So why do some survive and others not? Perhaps it’s because some have an edge? And a nuclear bomb went off in his mind, later to be detonated across the entire world.
But there was one oddity that Darwin noted about the disgusting lizards. He picked one up and threw it into the sea. This did not discompose the lizard very much: it is a strong swimmer and made its way back to land – where Darwin seized it by the tail and hurled it out again. He repeated this again and again, the iguana always returning to the shore where Darwin was waiting. He wrote in The Voyage of the Beagle: “Perhaps this singular piece of apparent stupidity may be accounted for by the circumstance that this reptile has no enemy whatsoever on shore, whereas at sea it must often fall prey to the numerous sharks, hence, probably, urged by a fixed and hereditary instinct that the shore is its place of safety, whatever the emergency may be, it there takes refuge.”I