What causes butterflies to flutter and flit up and down in the charming way they do?
鈥� Apart from flight, butterflies use their wings for temperature control, adjusting themselves to shed or absorb warmth.
These actions tend to be conspicuous, which creates selective pressures for species to advertise themselves as vividly as possible to their own species, or warn predators that they are unpleasant to eat.
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Such selection favoured flat, exaggeratedly conspicuous wings, which in turn constrains styles of flight, dictating larger, slower flapping movements than the compact, high-frequency wing vibrations of their ancestral moths.
The visual impression that butterflies' style of flight conveys is important; they emphasise it by up-and-down flapping of their billboards, and by individual styles of aerial dancing. This advertises their quality as mates, and provides recognition clues to their own kinds. For example, long-distance migratory butterflies such as monarchs don't fly like gliders in jungle clearings, or like clouded yellows dancing and dipping over alfalfa fields to attract mates, or leisurely Acraea species that only stupid birds taste twice.
Jon Richfield Somerset West, South Africa
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This article appeared in print under the headline 鈥淔ritillary flitter鈥�