Caffeine Foils Snails

By Marcia Wood
June 26, 2002

Caffeine can repel or kill snails that might otherwise eat and ruin plants, Agricultural Research Service scientists report in the June 27, 2002 issue of the scientific journal Nature.

An environmentally acceptable, natural compound, caffeine has great potential as an alternative to today's snail- and slug-killing chemicals. That's according to Robert G. Hollingsworth, a research biologist with the agency's U.S. Pacific Basin Agricultural Research Center in Hilo, Hawaii.

Hollingsworth conducted caffeine studies in collaboration with research entomologist John W. Armstrong at the Hilo Center and Earl Campbell of the U.S. Fish and Wildlife Service, Honolulu.

The idea of using caffeine to quell pests isn't new. But Hollingsworth and colleagues apparently are the first to report its prowess in clobbering pesky molluscs such as Hawaii's orchid snail, Zonitoides arboreus. The tiny snail is a common and costly pest to growers of Hawaii's colorful and exotic tropical orchids. These orchid farms are world renowned for the quality, quantity and variety of the flowers that they produce.

In preliminary experiments at his research greenhouse in Hilo, Hollingsworth applied a 2 percent solution of caffeine in water as a spray to the coconut husk-chips material in which orchids are grown. This growth medium, called coir, was infested with the tiny snails. The scientists found that the caffeine spray killed up to 95 percent of the snails.

In another experiment, the researchers showed that growth medium treated with the 2 percent caffeine solution had only 5 snails, when checked 30 days after the spray was applied. That's in contrast to the 35 snails that they found in growth medium that had been treated with a standard dose of metaldehyde, a common molluscicide.

Future investigations will provide further details about the ability of caffeine sprays to protect floral crops from marauding molluscs. Caffeine, a naturally occurring compound in coffee and chocolate, for example, is ranked "generally recognized as safe" by the Federal government.

ARS is the U.S. Department of Agriculture's chief research agency.