As we celebrated Olympic success in the summer of 2012, our butterflies were experiencing their worst season on record.

Two poor springs were partly responsible and with the possible exception of grassland species such as meadow browns, most others fared badly.

Two weeks ago I wrote that white butterflies were scarce again this year. But wow, what a difference a fortnight makes as whites have really built up splendidly everywhere. On 1st August, our hottest day, I went to Deen City Farm in Morden to be greeted by clouds of both large and small whites, the most I've seen in years.

They were indulging in a phenomenon known as 'mud-puddling', whereby on very hot days butterflies congregate in numbers on damp patches of ground especially if they contain animal droppings and urine. This is what occured at the farm in an enclosure housing cows and goats that had liberally sprinkled the ground with droppings, so numerous white butterflies, wings quivering, and resembling flotillas of yachts probed the wet earth.

Butterflies do this because they need not only moisture and nectar but vital salts and minerals contained in the droppings to help in their reproductive activities.

We do not often see this behaviour in Britain but in the tropics, vast numbers of butterflies cluster together to mud-puddle in rain forest clearings. There is even a species of tropical butterfly that relies solely on the droppings of leopards from which to imbibe the required chemicals.