Michael Bywater: In the dead of night, menacing us on our doorstep. That's Nature for you

Twins. Nine-month-old babies. Attacked. Partly eaten. By foxes. In Hackney. Unspeakable for their mother, and (as they so often say, because it's so often true) it could happen to any of us. Hackney: inner city, a bit run down, you might expect something like that in Hackney while simultaneously hoping you're wrong. But somewhere nice?

Well ... a few miles down the road and it doesn't get much nicer than Wimbledon. "Villagey," say the residents. Man and Nature living in harmony. They gesture towards the Common. Birds tweet. Undergrowth soughs in the gentle breeze. The word "bosky" is deployed. Here are the houses, nicely kept and in their place. Here are the shops, in their place, too. And there, the Common: Nature, in its place.

Walkers walk. Dogs (called Humphrey, not Tyson) frisk. The best of both worlds. Nature, in Wimbledon and in thousands of places just like it, is a resource, a recreation. The Common, like Hyde Park, Central Park, all the other Parks, is a lung – a refreshing but essential component of the idea of the city, without which its inhabitants would languish and grow pallid, feral and Dickensian. Parks are to Nature what bouillon is to an ox: a nourishing confection, free of death, hair, hoof and fibre, carefully reduced to its restorative essentials.

But Nature has other ideas.

Not so long ago I was staying overnight in Wimbledon and around 1am felt the need for a walk. Off I strolled down the civil darkened street. After a while I felt that odd prickle denoting unexpected company. I turned round expecting ... what? Whatever it is we expect when we turn round in the street in the night. What I saw was Nature: a large dog-fox. It stopped dead and glared at me. I took a step towards it. Unthinkably, it took a step towards me. In some inarticulate bit of my reptilian hindbrain, battle had been drawn. I took a step. It took a step. An ancestral memory of open jaws flying towards my throat scared me badly. Could it smell my fear? I could certainly smell it. Rank as a fox is not just an idiom.

Eventually I turned coward. "Good dog," I muttered, as though, by some sympathetic magic, I could name it into being something else: a Humphrey, of course, not a Tyson. Then I turned and walked – very slowly – away. It should have been a beautiful sight. It was not. It was frightening, and nasty, and wrong, like anything is nasty when it is in the wrong place.

The Hackney infants are one horrible reality of a more general (and ancient) idea: that we're here, clustered in our cities, under sufferance. Nature is waiting to get us. The barbarians (who are always at the gate, just under different names) are Nature's heralds. They can't speak properly: "Ba ba ba ba," they gibber. They are bearded, halfway houses between man and beast. Let them in without making them learn to speak like us, and Nature, with its beasts and fangs and hair and jaws and stealth and trumpeting cries of triumph in the night, will surely follow.

Nature may look as though it's out to get us, but we've been out to get Nature for a couple of thousand years at least – and, inadvertently, offered it a tempting home. The fox, driven from its traditional hunting grounds by agribusiness and Abu Ghraib-style chicken sheds, mooches into town. The waste. The McPickings. Nor should a fox – which, like us, will kill for sheer fun, way beyond its needs, as anyone who's seen a chicken run after Reynard has visited will confirm – be expected to distinguish between a human baby and any other source of food.

Nature is not us. We are just part of the system. We're so used to getting-to-eat that the possibility of joining the great majority, The Eaten, is both absurd and repulsive to us. Even the knowledge that a city-dweller is never more than 20 yards from a rat shocks and horrifies us, and it's not because of what the rat might do; it's the fact that they're here, in our space that upsets us. Mice in the wainscoting, squirrels under the eaves, a rat in every direction, slugs up the wall and, thankfully rarely but horribly at all, foxes eating our babies: if despite all our efforts, the buggers are still here, then what's the point?

And yet – in the West in general and in Britain in particular – we've managed to get ourselves all loved-up about Nature. We see our lives as artificial, and Nature as somehow real. Without ever asking ourselves whether the "real" is inherently better than the "artificial" we've fallen into a terrible post-Romantic fantasy about Nature as mother, as respite, as beauty and, most recently, sacred trust.

I say "post-Romantic" because at least the Romantics had, at the back of their minds, the idea of the Sublime, essential components of which were fear and threat. Rousseau, the begetter of Romanticism, said that what he needed in a vista was the sense of something terrible: not that far removed from the Garden of Eden (where the serpent lay in wait) or in Paradise (guarded by the enforcers – in celestial hi-vis tabards? – by an implacable God). We might note, too, that both Paradise in its original sense and Eden itself were walled and gated gardens. Beyond lay the wilderness: literally, wild.

Ruin at the hands of Nature awaits us, whether from the passage of time itself or from the depredations of climate (The Day After Tomorrow), Nature-perverted-by-Man (The Day of the Triffids), Nature-reclaiming-its-territory (Anaconda, the greatest Big Snake Movie ever made), Nature-going-about-its-business-heedless-of-puny-us (Eyjafjallajokull and its ancestor Vesuvius, which we now have to re-cast as a punishment by filling our dug-out Pompeii with an improbable number of speculative brothels). We can be threatened by Nature-as-alien (The War of the Worlds) or simply by going away altogether, as in Alan Weisman's The World Without Us.

In the end, still, the majority of the people in the world will be done for by Nature's most indomitable achievement: the bugs. A statistician might define Earth as The Planet of the Bacteria. We may never be more than 20 yards from a rat (and now, perhaps, a fox) but we are inhabited by bacteria.

We are all at war with Nature, although it becomes explicit only occasionally, as it did in Hackney this week. Some of us (environmentalists, climate change activists, moralist and food-intolerants of every shade) are at war with human Nature. Some are at war with Nature as being Everything Else But Us. Plague and famine, pesticides and fertilisers, salination and irrigation, deforestation and factory farming: all battles in that war. But Nature is one of those words – like "traffic" and "crowds" – that we use to distinguish ourselves from a group of which we are inarguably a member. Whether it be foxes or bacteria, rats or volcanoes, the war on Nature is one we can never win. For we have seen the enemy, and we are part of it.