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Most commercial products for snail and slug control contain either metaldehyde or methiocarb as the active ingredient, the residues of which are not permitted in food crops in the United States. We have discovered that solutions of caffeine are effective in killing or repelling slugs and snails when applied to foliage or the growing medium of plants. Because caffeine is a natural product and is classified by the US Food and Drug Administration as a GRAS (‘generally recognized as safe’) compound, it has potential as an environmentally acceptable alternative toxicant for the control of slugs and snails on food crops. While field-testing caffeine as a toxicant against an introduced frog pest that infests potted plants in Hawaii, we discovered that large slugs were killed by spray applications containing 1–2% caffeine. To test whether caffeine solutions could be used to remove or kill large slugs that attack potted plants, we allowed Veronicella cubensis (Pfeiffer) to bury themselves in the soil in the pots, and then thoroughly wetted the soil with a 2% caffeine solution. After 3.5 h, only 25% of the slugs remained in the soil; after 48 h, all slugs had left the soil and 92% were dead.