In earlier experiments soft, “plasticine” modelling clay was readily consumed by slugs. Therefore, a method for determining the grazing activity of Arion lusitanicus using plasticine baits was tested in the field. Plasticine was exposed on the surface of the soil in small trays shielded from mice by wire mesh screens. After several days of exposure, the quantity of plasticine consumed was determined by weighing. Laboratory experiments showed that the amount of plasticine consumed is proportional to slug body mass, plasticine is eaten over a wide range of temperatures between 6–25°C, and the presence of alternative vegetable food does not decrease consumption. In the field, consumption of such baits was positively correlated with slug numbers and revealed variation in slug grazing activity between sites during the course of a season. The use of plasticine baits is recommended for establishing slug feeding activity in the field. This is probably the best method available to date for quantitative studies. Plasticine was also eaten by several other species of slugs and snails.