Nature’s population explosions

WE are seeing an irruption of painted lady butterflies just now.

The insects hail from north Africa, where rains in the Atlas Mountains have led to a butterfly explosion. A single Moroccan field had 150,000 caterpillars. Pressure of numbers forced the insects to move, en masse, into southern Europe, where they bred. Their offspring, in turn, have come north, and painted-ladies are laying their eggs on Irish thistles. The generation they will produce here is doomed. All will perish during our cold Irish winter, a depressing thought. Hibernation, at the egg or adult stage, is the norm for our native butterflies, but such behaviour is unknown to tropical species; they don’t have winters.

Nature is seldom wasteful, so why does she allow butterflies to behave like this? Irruptions are a response to desperate situations. Dramatic fluctuations in animal numbers are rare in the tropics, but they’re the norm on the tundra and taigas of northern latitudes.