Standard metabolic rate (SMR) and resistance to body dehydration (BD) are important physiological traits that have an effect on water balance and the amount of energy available for activity and production, and thus could contribute to variation in life history traits expressed across a range of environments. Few studies have tested whether SMR and BD show consistent between-individual variation in molluscs. Significant repeatability of SMR and BD indicates that the traits might be heritable and therefore a possible target for natural selection, so describing the repeatability of SMR and BD is important in studies of phenotypic variability. Here, we studied energy metabolism (body mass-corrected SMR) and the change in the scaling relationship of SMR and body mass in response to time between measurements in the giant garden slug Limax maximus. Limax maximus is one of the most invasive terrestrial molluscs, with a wide geographical distribution, and is considered an important pest of horticultural and agricultural crops. Our results show that L. maximus follows the expected relationship of increasing SMR with increasing mass, but the scaling exponent varies through time and is different from that described for other gastropods. We also found significant inter-individual variation in VCO 2 Mean, VCO 2 Min, VCO 2 Max, and BD (τ=0.25, 0.29, 0.24, 0.22, p<0.05, respectively), and significant repeatability of body mass (τ=0.90). To our knowledge, this is the first comprehensive analysis of the repeatability of body mass-corrected SMR and BD in terrestrial slugs. Our results suggest that energy metabolism and water balance could potentially respond to selection.