You don't get nature on your own terms. You don't get life of any kind on your own terms: a sermon that has been preached to generation after generation by the stinging nettle. The provokers of childhood tears grow up to become a plant avoided or cursed by adults: the amount of pain it can deliver always an unpleasant surprise.

We hate nettles, but they follow us wherever we go. That's because nettles are peculiarly happy on land that bears a human footprint. They love rich, fertile ground: cattle pens, middens, dumps and graveyards. They are particularly fond of anywhere close enough to prairie farming to get the benefit of the fertilisers without meeting the wrath of the herbicides.

But nettles bring us great gasping vistas of beauty, for all that they do so vicariously - they are the resort of choice for our loveliest common butterflies. In season my garden is visited by commas and small tortoiseshells, peacocks and red admirals: a tribute to the essential gardening skill of letting the nettles thrive.

Humans, forced to confront nettles across the millennia, have found uses for them, particularly in extreme circumstances. You can eat them - they are an essential ingredient, for example, in St Columba's soup. The gorgeous cheese Cornish Yarg is wrapped in nettles. In the Second World War, the English used nettles as subsistence food while the Germans used them to make military uniforms.

Nettles also have a therapeutic value. The Romans brought nettles of their own to Britain, to rub on the skin when cold; Gypsies use them as a specific against arthritis; others have used nettles to alleviate all kinds of joint-pain. All of which makes the sudden rise in nettle numbers something worth celebrating.

The wild world is vital to us all, not for only its own sake but because biodiversity is essential for the future of the planet. It's good to know that these plant increases, of which the nettle is one, have mostly been the result of the set-aside system, under which land is let off intensive management and permitted to do what it wishes for a season or so.

The problem is that set-aside has already been abandoned all over Europe. The benefits of set-aside to nettles, and to the biodiversity of our entire continent, are all in the past tense. That's conservation for you: the good news is that we have the figures to show how something increases biodiversity; the bad news is that we have already stopped doing it.

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