Reducing numbers or populations of the Iberian slug (Arion lusitanicus)in private gardens in Norway

Abstract: Sixteen gardens in South-eastern Norway were divided into 4 groups of 4 gardens. Intreatment 1 (untreated control) nothing was done to reduce slug numbers. In treatment 2(‘killing’) the owners were encouraged to collect and kill as many slugs as possible. In treatment3 (habitat manipulation) owners were encouraged to change their garden so that an area of about20cm close to the ground was kept as open and dry as possible. Treatment 4 (extended habitatmanipulation) included treatment 3 but also by removing of potential overwintering sites such asopen compost, heap of stones etc. A reduction in the number of slugs was observed in all theyears and in all treatments from June to September, probably due to natural mortality. The meannumber of slugs was always lowest in treatment 2, in the third year showing a significantreduction of more than 80% from the control. In treatment 4 the mean reduction of slugs (notsignificant) was almost 40% during the third year. In treatment 3 the mean reduction (notsignificant) was about 55% during the third year. In conclusion, creating a garden not favourableto the Iberian slug can reduce the population without using molluscicides.