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Snails and slugs prefer decaf

By Bill Davis
Special to CNN

(CNN) -- Morning coffee won't pick up a snail's pace. In fact, caffeine may be poisonous to slugs and snails -- a finding that may lead to the development of more environmentally friendly pesticides, researchers said Wednesday.

A study in this week's issue of the journal Nature found that slugs and snails are killed when sprayed with a caffeine solution, and that spraying plants with this solution may prevent the slimy mollusks from eating them.

Scientists in Hawaii came upon the results almost by accident.

"We were looking for a solution for frogs," said Earl Campbell of the U.S. Fish and Wildlife Service in Honolulu. Campbell and colleagues were testing caffeine sprays to control coqui frogs, a problematic invasive species, when they noticed snails and slugs were also affected by caffeine.

Researchers found that when they sprayed an area of soil with a 2 percent caffeine solution, slugs and snails would either crawl away from the treated ground or die.

Further research showed that slugs preferred to eat plain cabbage leaves rather than leaves treated with a caffeinated spray. Similar studies found that more snails left planted areas treated with caffeine when compared to areas treated with a standard snail repellent.

The findings "aren't something that surprises me," said Campbell. "There's data in frogs, fruit flies, and mosquitoes" that suggest caffeine may be toxic to these animals. The researchers found that large doses of caffeine slowed the snails' heart rates and made contractions irregular.

But don't go pouring coffee on your garden; the average cup of joe contains only about 0.05 percent caffeine -- much less than what did in the snails.

Caffeine offers promise for snail and slug control, the researchers said, because it is labeled GRAS (generally recognized as safe) by the U.S. Food and Drug Administration.

Commercially available slug sprays contain strong chemicals that are regulated by the FDA and are not allowed in food products, they said. This means that these sprays cannot be used on any plant that humans will eat.

The researchers said the caffeine solution did not damage the foliage on some of the plants used in the experiments, although it did yellow the leaves of other plants, including lettuce. They said adding an agricultural polymer to the solution may help alleviate the problem.

Although two caffeine-containing pesticides have been developed, neither is on the market yet.


• Nature

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