This study investigates the effect of food distribution on the selection of foraging habitats, and the relationship between food availability, diet, ambient temperature, activity, use of shelter and energy budgets, in a termite-and ant-eating mammal, the echidna, Tachyglossus aculeatus. In two Nature Reserves in the wheatbelt of Western Australia, 10 adults and six juveniles were radio-tracked for II months during 1988. Animals were weighed monthly and their fresh faeces collected for dietary analysis. Available termite and ant energy was measured simultaneously in habitats where the echidnas foraged: woodland, mallee**, shrubland and heath. Termite energy formed the principal food of echidnas, possibly because of their greater abundance. Highest ingestion rates of termite energy during the hottest time of year may reflect increased moisture requirements. Adult animals preferred woodland and mallee for foraging, possibly because termite and ant energy was highest there. Juveniles exhibited no obvious habitat preference. Echidnas were active year-round, with foraging peaks during spring and autumn, and animals gained weight then. Despite termite energy being highest in winter, echidnas were in negative energy balance during this period, possibly because they make smaller foraging efforts and have higher thermoregulatory costs. Foraging was principally nocturnal in summer, and mixed nocturnal/diurnal in winter. No foraging was observed below 9° and above 32°C, with a preferred range of 16–20°C. Echidnas were not apparently food-limited because: (a) both adult and juvenile animals maintained, or gained, body weight even when termite energy was low; (b) juveniles foraged anywhere, irrespective of habitat, but still gained weight; and (c) there was no evidence for hibernation by wheatbelt echidnas, unlike in other parts of Australia where echidnas routinely hibernate in winter, possibly in response to food shortage. However, echidnas did show signs of short-term torpor. Echidnas were active throughout the year, possibly because food was unlimited, and because use of subterranean shelter reduced thermoregulatory costs. The results of this study suggest that food distribution and ambient temperature play an important role in influencing daily and seasonal foraging activity in wheatbelt echidnas.