Disclosed are phosphonic acid formulations comprising i) a phosphonic acid of the formula R-P(OH)2(=O), in which R represents alkyl which is monosubstituted or polysubstituted by identical or different substituents from the series consisting of PO3H2, CO2H, OH, NH2, CN, halogen, alkylamino or dialkylamino and which is optionally interrupted by 1-6 heteroatoms from the series consisting of N, O, S, P, with heteroatoms not being linked directly to each other； and/or the ammonium, alkali metal, alkaline-earth metal and/or iron salts thereof； and ii) methiocarb； characterized in that the amount of i) is from 0.5 to 10% by weight and the amount of ii) is in the range of from 0.1 to 1 % by weight of the formulation. Preferred phosphonic acids include compounds such as etidronic acid. Also disclosed is the use of a phosphonic acid formulation as defined above for controlling terrestrial slugs and snails, characterized in that the formulation is applied to the habitat of the slugs and snails.
