What makes a glow-worm glow?

Glow worm - the female glow worm is equipped with one of the most marvellous lightning systems in the world. A wingless beetle she crawls about at night eating small insects. But on the lower side of her abdomen she possesses a "lantern" which she uses to signal to her winged mate flying above. This "lantern" has a transparent layer of skin like the lens of a lamp. Behind this is an oily layer of tissue which produces the light by a chemical process and a second layer which acts as a reflector. The glow worm is able to control this remarkable bright light, using it only at certain times to attract a mate. In fact the light is a female call and the male has particularly the large eyes to enable him to see the signal. An abundant supply of water and oxygen is needed by the glow worm to maintain the chemical activity producing the light. For a time even the insect's eggs are luminous. Glow worm, which are about half an each long, are natives of Europe. Other beetles with built in lightning systems are called fireflies. Both male and female fireflies have wings and use lanterns to signal to each other and to warn off night birds who seem to find them unpalatable. The most famous are the large and brilliant cucujos of tropical America. On special occasions young women fasten them to their dresses where they shine like glowing gems.

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