Thorny Devils do not eat anything but ants. They prefer several species, but are especially indifferent to very small ones (Iridomyrmex flavipes). Eat from 24 to 45 ants per minute. Sometimes, accidentally, along with the ants, small stones, grains of sand, chips, tiny flowers or eggs of insects are swallowed. At one time, animals are able to eat a large number of ants, from 675 to 1000-1500 and even up to 2500. The presence of Thorny Devils is indicated by their excrement.
The feces of these lizards are black, glossy, slightly elongated spherical. Neat little heaps are often found either in open spaces, or among scanty vegetation. Each individual has a specific place for defecation, separate from the places of lodging or feeding. Accumulations of faeces indicate that Thorny Devils often return to such places, several days in a row.