Nature Studies by Michael McCarthy: Don't underestimate the power of tiny things
Friday 09 September 2011
It is a strange fact, not often remarked upon and indeed, strongly counterintuitive, that among the wild beasts of Africa, herbivores are much more dangerous to humans than carnivores. Elephants, hippos and buffaloes (or perhaps we should use the old-Africa-hand singular form of the plural, buffalo), which are all vegetarians, are far more likely to kill you than meat-eaters such as lions, leopards and even crocodiles. This is because they will not be killing you as prey; the great herbivores will kill you for being an irritation or a perceived threat if you intrude upon their territory (especially, if you get between a mother and her young). They are so whoppingly big and fearless that their way of dealing with you is simply to take you out, and once they head for you, it will take a rocket-launcher to stop them.
All the people of rural sub-Saharan Africa know this. If you talk to poor African farmers, it can come as a shock to realise how deeply they hate the elephants they have to live alongside; we may revere them in Europe as noble and dignified, but for farmers in somewhere like Namibia they can be monsters which can destroy your year's crops in a night and kill your kids on their way home from school, and I've talked with families where both of these things have happened.
That is our normal idea of power, raw power, in the natural world: big beasts. And I bring it up because I want to talk about the opposite, which is much less evident but ultimately even more effective: the power of tiny things.
If you walk into any urban park this weekend, or walk out into the countryside, you will see that some trees have already turned brown, even though autumn has barely begun, and all the rest are green. If you look more closely at the desiccated and crumpling leaves, you will see that the trees concerned are all the same species: horse chestnuts, conker trees. Then you will notice that the leaves are not actually dead; rather, they are covered with a mass of disfiguring brown scars.
These have all been caused, and the horse chestnuts of southern England all turned prematurely brown (with those in the rest of the country soon to follow), by a tiny, specialised insect: the horse chestnut leaf-miner moth, Cameraria ohridella (I like think of it as Horridella). Ten years ago, it was unknown in Britain; it seems to have come from the Balkans (where horse chestnuts originated) and spread across Europe, arriving here in 2002. Since then it has colonised much of England and Wales, and is heading unstoppably for Scotland. It has transformed the landscape, and the townscape, too. Go out and look at it. Horse chestnuts are planted everywhere as our favourite decorative tree and now their foliage is over, two months early. Yet the organism which has brought this about is minute: the moth caterpillar which "mines" or burrows into the leaf in the springtime is smaller than a grain of rice.
It has had such an effect because of the strategy nature has evolved to make tiny things powerful: profusion. On a single horse chestnut tree in your high street or local park there will be tens or even hundreds of thousands of leaf-miner moth caterpillars tunnelling into the leaves. The smaller the organism, the greater the numbers. Eagles have a couple of chicks, or only one; diminutive blue tits have a dozen chicks, as many will die, but with a dozen, some will survive. To perpetuate small species, nature will countenance the deaths of numberless individuals.
As they began to perceive this, Victorian thinkers, still striving to see a divine purpose in nature, found it very troubling:
So careful of the type she seems,
So careless of the single life....
lamented Tennyson, in In Memoriam, feeling his Christian faith shaken by the ruthless sacrifice inherent in the survival strategy of profusion.
But profusion in small things works, and, ultimately, it trumps individual size. Yes, an elephant can trash a field of crops – but not half as effectively as a swarm of locusts.
Or consider this: it used to be thought at the height of the Cold War that a nuclear exchange would kill half the population of Europe, through atom bombs with the power of millions of tonnes of TNT. Yet between 1347 and 1351, pretty much half the population of Europe was wiped out, in the Black Death, by the bubonic plague bacillus, which you need a microscope to see.
The power of the single big beast is illusory. Never mind elephants. Go and look at your local conker trees, all dropping their conkers now from a mass of brown leaves, wrinkled and finished long before their time; you will understand that real power in nature, the power to reshape the world, lies with the tiny things in their endless numbers.
King of the jungle? Not what you think
Say that the most dangerous animals in Africa are the elephant, the hippopotamus and the buffalo and you instantly invite a follow-up question: which is the most dangerous of all?
You may be surprised at the answer: several authorities affirm that more deaths are caused annually by hippos than by any other African animal. They might look cuddly and faintly comic; they're not.
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