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Wednesday, 26 June, 2002, 18:16 GMT 19:16 UK
Caffeine 'repels slugs'
Coffee (BBC)
Caffeine: A lethal neurotoxin to garden pests
Scientists have stumbled on a secret weapon against snails and slugs.

They have discovered the garden pests are poisoned by caffeine.

A strong cup of coffee is enough to send the creatures into a writhing frenzy, followed soon by death.

Scientists think caffeine acts as a potent neurotoxin against the pests.

The finding may be of use to gardeners and commercial growers. Slugs and snails are notoriously difficult to deter from attacking plants.

The chemicals currently used to control them are not permitted as residues on food crops.

Caffeine - regarded as safer and more environmentally acceptable - could be very useful in pest control.

Special brew

The discovery was made by scientists at the US Department of Agriculture's Agricultural Research Service in Hawaii.

They were testing a caffeine spray against frog pests when they noticed slugs were dying.

Follow-up studies showed that a 1-2% caffeine spray was enough to kill snails and slugs.

Even at concentrations about 100 times weaker, the slugs lost their appetite.

A cup of instant coffee contains about 0.05% caffeine, while brewed coffee contains more.

Lead researcher Dr Robert Hollingsworth says because caffeine is a natural product and is classified by the US Food and Drug Administration as safe, "it has potential as an environmentally acceptable alternative toxicant for the control of slugs and snails on food crops."

Natural high

There is a catch. Caffeine at 2% concentrations can damage the foliage of plants or cause yellowing.

It may be possible to overcome this by mixing caffeine with a polymer, say the researchers, who report their findings in the journal Nature.

But not everybody is convinced that caffeine is environmentally friendly.

Dr David Bohan, of the UK agricultural research institute IACR-Rothamsted, told BBC News Online: "1-2% is a very high concentration of caffeine.

"That might be potentially damaging to plants and invertebrates other than slugs such as insects."

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The BBC's Sue Nelson
"Caffeine could be an environmentally friendly pesticide"
See also:

30 Aug 00 | Science/Nature
29 Oct 01 | Health
10 Oct 01 | Health
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