Weather Watch

Have winds in the Bay of Biscay blown millions of butterflies towards our shores? Or are butterflies brighter than we think?

The trouble with being a butterfly is that you cannot function if the temperature falls below 14C. Feeding and mating are simply too much for them in the cold. While butterflies undeniably do get blown around by the wind, there is also a good deal of evidence that they fly purposefully in search of food and warmth.

The small tortoiseshells, millions of which have arrived in Norfolk in recent weeks, generally start their lives in southern Europe, then fly north through France in search of food. While air currents may help them, many journeys are taken against the direction of the winds. Painted ladies are particularly determined, flying from Africa through the Pyrenees and France in search of better conditions.

The biggest puzzle, however, is the monarch butterfly, which occasionally crosses the Atlantic to be seen in Britain. But how? It cannot use the high winds of the upper atmosphere - they are far too cold. They cannot take a rest by sitting on the sea, and they'd be spotted on boats if they tried to hitch lifts in large numbers. They arrive in good condition, too.

Caterpillars, incidentally, can hang-glide using their own silk. But that's another story.