We investigated the whole-body crude nutrient (fat, protein, ash) and mineral (Ca, P, Mg, Na, K) composition of mustached bats of three different groups: animals from the wild (n = 6), and animals from captivity on an unsupplemented feeding regime of mealworms (n = 7), and on a feeding regime in which the mealworms were kept on a mineral substrate prior to feeding (n = 6). It was shown that mealworms from the mineral substrate had higher Ca contents than mealworms from the conventional substrates. In an earlier study, differences in bone mineral density had been found between the groups. These differences, however, were not reflected in differences in whole-body composition. Captive animals showed a larger variation in body weight and fat content, indicating potential shortcomings of the dietary and husbandry regime.