Abstract: Activity and food consumption were simultaneously monitored in populations ofknown density (20 or 40 animals m-2) and biomass of adult slugs Deroceras reticulatum (Müller,1774) and adult snails Cantareus aspersus (Müller, 1774), kept in mini-plots under semi-naturalconditions. Food consumption of turnip roots was monitored daily in terms of dry weight. Theactivity of the populations was monitored using time-lapse video techniques to record themovements of the animals. To obtain a comprehensive measure of the activity over the timecourse, the numbers of active and feeding animals registered at 30 min intervals were integratedover time using the formula for the calculation of the “area under the disease progress curve”(AUDPC), thus allowing expressing the intensity of activity and the intensity of feeding activityof the populations by single values over each 24-hours period. Daily food consumption per gramof biomass was independent of population density for both species, and it was nearly 3 timeslarger in the slug than in the snail; however, food consumption per plot was nearly 10 timeslarger in the snail because of their bigger size. On average, the activity level over the year washigher and less variable in D. reticulatum populations than in C. aspersus populations. The dailyintensity of activity and daily intensity of feeding activity showed significant correlations betweenthem and with food consumption (g d.w./g biomass/day), but activity explained only a limitedamount of the variability in food consumption.