Tamar Haspel, who writes the very fun blog Starving Off The Land, once wrote that she was disinclined to bait slugs and snails with beer because it was too much like buying them a beer. When you factor in who-in-their-right-mind-would-bait-them-with-the-good-stuff,-so-let's-just-go-to-the-store-and-get-a-sixer-of-Old-Milwaukee, you realize that she's right. You are buying them a beer, which seems a ludicrous thing to do when they are your enemy, after all, and one with whom diplomacy has no value.
But would you buy them a cup of coffee? A very dilute cup of coffee?
It turns out that even in very dilute solution, caffeine is a great poison for slugs and snails. To wit: "In this study, caffeine is shown to act as both a repellent and toxicant against slugs and snails. This research is the first to document the potential of caffeine as a molluscicide. A drench treatment using a 1% or 2% solution of caffeine caused 100% of slugs (Veronicella cubensis) to exit treated soil, and the majority of these slugs subsequently died from caffeine poisoning. A 2% solution of caffeine applied to the growing medium of orchids killed 95% of orchid snails, (Zonitoides arboreus), and gave better control than a liquid metaldehyde product representing the standard commercial control for this pest. Using leaf-dip bioassays, we discovered that slugs tended to avoid feeding on plant material treated with caffeine solutions 0.1%, and caffeine solutions as low as 0.01% significantly reduced overall feeding by slugs. Due to concerns about chemical residues, available molluscicides generally cannot be applied directly to food crops for control of slug and snail pests. Caffeine is a natural product which is approved as a food additive. Therefore, caffeine may prove useful for protecting food crops from slugs and snails." This is from an abstract written by R.G. Hollingsworth, J.W. Armstrong, and E. Campbell and published in The Annals of Applied Biology, Volume 142, Number 1, 1 February 2003 , pp. 91-97(7).
Of course, you'd have to reapply it every time it rained, but I make coffee every day, and I can see myself sacrificing a cup to the sprayer and getting out there with it. It would sure beat picking them off by hand.
This will give new meaning to the term 'slugging back a cup of coffee'. I almost can't wait to try it.