Michael McCarthy: To hear a bird, see an insect and to know May is here

There is an intensity of loveliness in the natural world which is unmatched at any other time of year

So the month of May has come round again, the month that medieval England adored above all others for its freshness and its beauty, associating it with the Virgin Mary. In our urban lives, we may notice very little of the beauty now, but if you make the effort and leave the concrete city and the fumes behind, you can still see why Chaucer and his peers were so moved.

So the month of May has come round again, the month that medieval England adored above all others for its freshness and its beauty, associating it with the Virgin Mary. In our urban lives, we may notice very little of the beauty now, but if you make the effort and leave the concrete city and the fumes behind, you can still see why Chaucer and his peers were so moved.

There is an intensity of loveliness in the natural world in May which is unmatched at any other time of the year: the iridescent green of the new leaves (which only lasts a fortnight), the sheer volume of birdsong, the bluebells like an azure smoke covering the woodland floor.

But it's not just pleasurable. Sometimes, this beauty is so profound that it triggers in human beings a singular response. It's as if we were in the presence of, or on the edge of, something transcendent, something far greater than us, something wholly good and wholly important - but not quite graspable in the normal way, not quite subject to rational explanation,

Down the centuries, this was by no means inexplicable to the Christian mind. It was simple: it was the visible glory of God, the divine nature clearly manifest in His creation here on earth.

But how do we account for these feelings when Christianity has gone? What are we to make of them after Darwin, when we know that the colour of flowers, and the power of birdsong, are merely adaptations brought about, at random, by the remorseless mechanism of natural selection, to aid organisms to reproduce? That is, presuming we still have these feelings.

Some people clearly do. But perhaps we hear much less of them today, because in a post-Christian world there is no easy channel for their expression. In the earlier part of the 20th century, this was something of a challenge for poetry. Edward Thomas, the sensitive and reserved poet killed in the First World War at the age of 39, tried in at least two poems to get to the heart of the transcendent experience nature sometimes gave him, without using the prop of religion.

One was "Old Man" (the name of a plant - "the hoar-green feathery herb, almost a tree") and the other "The Unknown Bird". A scent, in the one case, and a call, in the other, provoked in Thomas a deep spiritual longing, which he tried, but failed, to explain (but which he nevertheless registered magically.)

Philip Larkin was more successful in explaining the longing, although he did it not with nature, but with churches, which, as a bored atheist in the 1950s, he found himself perversely drawn to. In "Church Going" (arguably the greatest poem written in English in the last 50 years), Larkin determinedly works out, in purely humanist terms, exactly what it is that has attracted him, a cynical non-believer, to a run-down church building:

"A serious house on serious earth it is,
In whose blent air all our compulsions meet,
Are recognised, and robed as destinies."

(That "robed" is worth a Nobel prize for literature all by itself).

Yet even Larkin, much moved by the natural world, was unable to provide a rational explanation of why nature, rather than an old church with its attendant graveyard, should sometimes provoke in us a very powerful spiritual response.

Is this, perhaps, one of the greatest losses of the crumbling of Christianity, that with the natural world we now have understanding in abundance, but we no longer have meaning?

Some time, during this coming month of May, I will hear a bird, and see an insect, which provoke in me the feeling that I am suddenly in touch with something far greater than myself. The bird is the redshank, a long-legged wader of marshes and wetlands. Its call is three pure, liquid, descending notes, which are the very essence of wildness. The insect is the banded demoiselle, one of the damselflies: it is brilliant blue-green with broad bands of royal blue across diaphanous wings, quite astonishingly beautiful, like an insect designed by Fabergé.

I am always stopped short, by hearing the one, and seeing the other. They trigger in me feelings which - I feel instinctively - human evolution alone cannot account for. Sometimes I feel, in the presence of such beauty, that I'm at a half-open door, I'm on the threshold of something remarkable, something far profounder than everyday life, something which is wholly worthwhile, which has always been there and will always be there, and is behind everything else.

But what this may be, in this post-Christian world, I cannot tell.