Mean apparent dry mass absorption efficiency by P. auritus fed on mealworms was 0.853 (S.D.=0.4, n=43). Mean apparent energy absorption efficiency by P. auritus and M. daubentoni fed on mealworms was 0.90 (S.D.=0.007, n=8). The mean energy content of mealworms was 28.6 kJ.g-1 dry mass (S.D.=1.1, n=8), and that of faeces was 19.5 kJ.g-1 (S.D.=0.7, n=8) in P. auritus and 19.9 kJ.g-1 (S.D.=1.3, n=8) in M. daubentoni. Water content of mealworms was 61.1% wet mass (S.D.=1.4, n=173); water content of faeces was 73.3% in P. auritus (S.D.=6.8, n=76) and 72.3% (S.D.=7.0, n=42) in M. daubentoni. Oven-dried mealworms consisted of <1% ash, <1% carbohydrate, 31% lipid and 39% protein. We suggest that the dry mass unaccounted for (28%) represented chitin, of which 59% was apparently absorbed during digestion. Apparent absorption by mass of both lipid and protein by P. auritus fed on mealworms was greater than 90%. Cumulative post-prandial defecation was sigmoidal in both bat species with 50% (by mass) of faeces being voided within 4 h and 95% within 12 h of feeding. On the basis of previous measurements, using doubly-labelled water, of daily energy expenditure and water flux in free-living P. auritus, we predict that water intake via the food, as free water and as potential metabolic water, represents 20 to 40% of total daily water flux for P. auritus during lactation in the wild.