Metaldehyde is the traditional slug and snail poison that has been used since the 1940s. Highly effective but carries serious risks to dogs, cats, and wildlife. Being phased out in the UK and EU in favor of safer iron phosphate alternatives.
Slugs and snails. Metaldehyde is highly specific to gastropod mollusks. Does not affect earthworms, insects, or other soil organisms directly, though secondary poisoning of beetle predators that eat poisoned slugs has been documented.
Deadline M-Ps (slug pellets), Corry Slug and Snail Killer (metaldehyde version), Sluggo (note: Sluggo is iron phosphate NOT metaldehyde - check labels), various store brand slug baits. Always verify active ingredient on label - some brands have switched from metaldehyde to iron phosphate.
Moderate to high toxicity to mammals. EPA toxicity Category II-III depending on formulation.
Also toxic to cats, birds, and wildlife. Hedgehog deaths are a major concern in the UK, leading to the ban. If you have pets or wildlife, use iron phosphate bait instead - it is equally effective and completely pet-safe.
Why iron phosphate is better: Iron phosphate (Sluggo) provides equivalent slug and snail control with zero risk to pets, children, or wildlife. There is no practical reason for homeowners to use metaldehyde when iron phosphate is widely available. The only advantage metaldehyde retains is slightly faster kill speed (hours vs days).
If you must use it: Place pellets under boards, flower pots, or slug shelters where pets cannot access them. Use tamper-resistant bait stations. Apply sparingly - more bait does not mean better control. Water the area first to bring slugs to the surface.
Timing: Apply in late afternoon before slugs become active at night. Reapply after rain as metaldehyde dissolves in water (losing effectiveness but also contaminating soil).