Sunday, May 20, 2007
How Crystals May Help The Firefly To Survive
In parts of tropical Asia, you can see trees glowing in the dark - single trees where waves of light ripple from top to bottom and back again, and rows of trees where the light leaps from one tree to another.
This extraordinary effect is caused not by the trees themselves, but by the synchronised flashing of thousands of fireflies that have gathered in the branches. Look closely and you will find that each tree harbours a different species of these luminescent insects.
Why these mass displays occur is not fully understood. But biologists do know why fireflies flash when flying alone, and how they produce light.
Fireflies glow in order to find a mate. The male of one common species of North American firefly, Photinus pyralis, flashes regularly while flying. The female, watching from the ground, flashes back in a rhythm unique to its own species. The male recognises this signal and drops towards a new mate.
It is possible that the flashing light also serves as a warning mechanism, reminding would-be predators of the firefly's bitter taste. But it does not always work - certain frogs eat so many fireflies that they themselves glow.
Firefly 'lanterns' contain oxygen and a substance called luciferin. The chemical reaction between the two produces light. An enzyme called luciferase helps to speed up the process, and this in turn intensifies the light.
Where do crystals come into all of this? In the lantern is a layer of ammonium urate crystals, behind the light emitting luciferin. These crystals help to scatter the light and increase the effectiveness of this remarkable natural signalling system.