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A mocha latte might be your favorite way to start the day, but the same cannot be said for slugs and snails. According to a study published today in the journal Nature, caffeine solutions sprayed onto plants can deter and even kill the pesky mollusks. Farmers must often tolerate these destructive creatures because most pesticides are deemed too toxic for use on crops. The U.S. Food and Drug Administration classifies caffeine as "safe," however, prompting optimism that the substance could form the basis for an acceptable crop pesticide.
Robert Hollingsworth of the U.S. Department of Agriculture¿s Agricultural Research Service in Hilo, Hawaii, and his colleagues discovered caffeine¿s killer effect while testing it against a frog that plagues potted plants in Hawaii. The team noticed that slugs and snails, not the frogs, in the treated area were the ones that were dying. Further tests revealed that even a 0.01 percent caffeine treatment sprayed on plant leaves made them unpalatable to the mollusks. Solutions containing 1 to 2 percent of the substance killed them. (For comparison, a typical cup of instant coffee contains 0.05 percent caffeine.)
Exactly how caffeine kills the mollusks is not known, but the researchers posit that it may alter their neurological function. The chemical may not be effective against all garden pests, though. "Slugs and snails may be more susceptible to contact poisoning from caffeine than other animals," the authors write. "This is because caffeine is highly soluble in water, an important component of the mucus produced by the locomotive ¿foot¿ of mollusks." Clearly, mollusks get a slightly different kick out of caffeine than humans do.