METEOROLOGISTS have a soft spot now for butterflies. They became almost a part of our accoutrements following the rhetorical question posed by Edward Lorenz, the originator of chaos theory, in a famous lecture in the early 1970s: "Could the flap of a butterfly's wings over Brazil spawn the next tornado up in Texas?"
The aptness of Lorenz's lepidopteral paradigm is due in no small measure to the extreme fragility of these gentle creatures. Indeed, far from provoking distant meteorological disasters with a wing twitch, the average butterfly is more likely to become a victim of its local weather since it has constant need for uninterrupted sunshine.
Butterflies require sunshine for mobility. Being cold blooded creatures, they use the external heat provided by the sun to fuel the muscles used to flap their wings and fly. In cloudy conditions, the insect, like a kind of solar powered aircraft, is virtually helpless.
It is because of this external heat requirement that we see no butterflies in the very early morning, since it takes some time for heat from the rising sun to provide the energy required for flight.
Even during the day, at the slightest hint of cloudiness, the butterfly stops work immediately and hangs suspended from a leaf or flower, and only when the sun comes out again does the hunt for food resume. Most butterflies live only a few weeks and spend their short lives near where they were hatched, making the best of whatever the weather may be.
A few enterprising species, however, have developed the knack of doing something to improve their lot in this respect in vast numbers they undertake an arduous journey to a more congenial climate for the winter season.
Charles Darwin, on the Beagle, witnessed a migration off the coast of South America: a vast cloud of butterflies 600ft above the water, a mile wide and several miles in length. "They appeared in bands or flocks of countless myriads, extending as far as the eye could range and even with a telescope it was not possible to see a space. The seamen cried out: `It is snowing butterflies', and such, in fact, was the appearance."
In Europe the Painted Lady butterfly migrates to Africa in autumn, and in the United States the famous migration of the Monarch species is a regular feature of the calendar, its participants rivalling in theirs numbers the procession seen by Darwin.
Every autumn the Monarchs travel 2,000 miles from their summer homes in the northern US or Canada, to winter in the mellower conditions of Mexico, Florida or California.