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Old 29-10-2002, 03:27 AM
George D
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Default Snails and slugs

I just read this on the Arizona Arid Gardener list serve and thought someone out there might be

Given the way acidic coffee grounds are a great additive to our alkaline soils, I thought the
following was interesting. jk

From Nature Website
Caffeine kills slugs and snails.
27 June 2002


Humans have a new weapon in the eternal battle against slugs and snails - the double espresso.

Slugs and snails hate caffeine, researchers have discovered. The chemical could become an
environmentally acceptable pesticide.

Robert Hollingsworth of the United States Department of Agriculture's Agricultural Research Service
in Hilo, Hawaii, and his colleagues were testing caffeine sprays
against the coqui frog, an introduced species that infests potted plants.

They noticed that a 1-2% caffeine solution killed nearly all the slugs and snails within two days.
Concentrations as low as 0.01% put the pests off their dinner. A cup
of instant coffee contains about 0.05% caffeine, and brewed coffee has more.

Coffee grounds are already recommended as a home remedy for keeping slugs and snails at bay. Grounds
repel slugs, Hollingsworth found, but a caffeine solution is
much more effective, he says: "Slugs turn back immediately after contacting the [caffeinated soil]."

Caffeine is more effective against snails than the current commercial standard, metaldehyde. The
United States bans metaldehyde residues in food, but classifies
caffeine as safe. It may even qualify as organic, adds Hollingsworth.

Caffeine is likely to have an effect on beneficial insects
Peter Usherwood
University of Nottingham, UK

"I would expect caffeine applications to kill small snails and slugs, and repel the larger ones,"
says Hollingsworth. He envisages it being used in orchid greenhouses
and on fruit and vegetable crops.

Toxicologist Peter Usherwood, of the University of Nottingham, UK, thinks that caffeine is best
suited for use in domestic gardens. But he cautions that the
chemical's toxic effects are not limited to slugs and snails. "It's likely to have an effect on
beneficial insects," he says.

It's not known how caffeine kills the molluscs. Hollingsworth's team suggests that the chemical may
cause damage to the nervous system - they report that
caffeine-sprayed snails develop weak and irregular heartbeats, and slugs fall to "uncoordinated
writhing" before dying.

1. Hollingsworth, R. G., Armstrong, J. W. & Campbell, E. Caffeine as a repellent for slugs and
snails. Nature, 417, 915 - 916, (2002).

George D
Phoenix, AZ

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