Termite Digestibility and Water and Energy Contents Determine the Water Economy Index of Numbats (Myrmecobius fasciatus) and Other Myrmecophages

Digestibility by captive numbats for termites was determined by feeding trials to be 81%+/-1.2% for Coptotermes sp. and 64%+/-3.3% for Nasutitermes sp. Water, ash, and energy content of both the Coptotermes(0.96+/-0.099 mg(dry mass) individual(-1), 78.0%+/-0.36% water, 5.8%+/-0.31% ash, 23.1+/-0.19 kJ g(dry)(-1) total energy) and Nasutitermes(0.91+/-0.046 mg(dry mass) individual(-1), 76.7%+/-3.09% water, 7.5%+/-1.10% ash, 22.7+/-0.36 kJ g(dry)(-1) total energy) were similar to values measured previously for other termites and for ants and insects in general. Numbats have a slow passage time for termites (20-30 h), presumably to enhance the digestion of termites. The water economy index (WEI) was 0.2 for captive numbats feeding on Coptotermes and 0.25 for Nasutitermes, whereas the WEI measured for wild, free-living numbats was 0.29, which corresponds to a digestibility of 58%. The WEI of a myrmecophage diet is determined by the energy and water contents and digestibilities of termites and ants, in the absence of drinking. The WEI for numbats, and other termitivorous mammals as well as reptiles, is higher than would be expected for an animal-based diet because of their relatively low digestibility (58%-81%) for termites. A high WEI preadapts myrmecophages to survival in arid environments without having to drink.