Males of A. caerulea show a reversible colour change, controlled only by temperature. The Tyndall-blue of the abdominal spots and eyes changes to greyish purple with decreasing temperature (< 16° C), the reverse colour change occurs with increasing temperature (> 10° C), The colour change is possibly controlled by the same mechanisms as recorded in Austrolestes annulosus and Diphlebia nymphoides, although in A. caerulea it seems to be more rapid. Colour change and the special perching behaviour, as temperature-regulating mechanisms in A. caerulea males, and their adaptive value, are discussed.