An ingestible mollusc poison contains a simple metal compound, an activity enhancing additive such as ethylene diamine disuccinic acid (EDDS) and derivatives thereof, and a carrier material edible to molluscs. In one embodiment the active agent of the mollusc poison may be in the form of a metal complex of EDDS. The composition may be used alone or in conjunction with molluscicidal co-active agents and/or fertilizers.