The sperm contains an alkaloid that is distasteful to spiders. The chemical reaches every part of the female's body within minutes of mating and will protect her for the rest of her life.

This moth was released after the spider tasted it

The discovery was made by biologists at New York's Cornell University. "This classy moth gives his mate a gift she can really use, that keeps paying off every time her life is in danger," says Thomas Eisner, Professor of Chemical Ecology.

The male moth acquires the alkaloid from the rattlebox plant, which it eats during its larval stage. During courtship, two brushes on the male's abdomen release traces of the chemical into the air, allowing the female to choose the mate best equipped to offer the protection she needs.

Dangerous to gnaw

The biologists tested two sets of moths on wolf spiders and orb-weaving spiders. One group was fed on rattlebox plants, the other on pinto beans that do not produce the alkaloid.

Every moth with the chemical in its system was cut loose from the web by its captor and released. Moths without the alkaloid were killed and eaten.

The rattlebox moth is named after the plant it eats

The rattlebox - also called the ornate - moth, which is native to central Florida, alerts predators to its inedible nature through its elaborate flamingo pink, black and white colour scheme.

Spiders which ignore the visual warning are put off by taste: a frothy blend of alkaloid and air bubbles is extruded from the moth's thorax when it is disturbed.

When rattlebox moths mate they remain coupled for eight or nine hours. A female will have up to 20 mates in her 30-day lifespan.

All photographs copyright © 1999 Thomas Eisner