April 17, 2011

Flights of fancy

Image courtesy Ernst Vikne
I saw a common blue butterfly in my garden yesterday. Despite the name they're not all that common, and April is early to see them flying. There are far fewer butterflies around these days than when I was a child, so I count any of them as a blessing; and here was a beautiful azure insect flickering through the ivy covering our back fence.

Much commoner was the cabbage white (or, more properly, the large white) that was blundering about today. It's amazing how bad some butterflies seem to be at flying, but there's a good reason for it. Those that are unpalatable - that have evolved bad-tasting toxins to protect themselves from predation - advertise the fact with slow, ungainly flight. It is only the tasty varieties that need fast, evasive and direct flight, and the greater energy (and requirement for food) that such flight demands. Insectivorous bird species have generally learned which butterflies (and caterpillars) are worth eating; the cabbage white, and its larvae, are not.

Butterflies and moths have one of the most miraculous life cycles of any living thing. We're all taught at school that the caterpillar makes a chrysalis out of its own skin, emerging from it as a butterfly, but the details of its transformation are truly bizarre. Inside the chrysalis the caterpillar isn't merely growing wings, legs and a proboscis; it melts itself down into a kind of DNA soup, then reconstitutes itself from scratch as a new creature. The butterfly DNA, present in the caterpillar but 'switched off', is finally expressed.

Watch a one-minute, time-lapse film of a cabbage white emerging from its chrysalis and inflating its wings here. It's narrated by David Attenborough, so you know it's going to be good.