Mud-nesting wasps are found in all of the main biogeographical regions of the world(1-3), and construct nests that become petrified after abandonment, Nests built by mud-dauber and potter wasps in rock shelters in northern Australia(1,4) often overlie, and occasionally underlie, prehistoric rock paintings. Mud nests contain pollen, spores and phytoliths from which information about local palaeovegetation can be gleaned, Here we report a new application of optical dating(5-7), using optically stimulated luminescence (OSL), and accelerator mass spectrometry (AMS) C-14 dating of pollen(8) to determine the ages of mud-wasp nests associated with rack paintings in the Kimberley region of Western Australia(9,10). Optical dating of quartz sand (including the analysis of individual grains) embedded in the mud of fossilized nests shows that some anthropomorphic paintings are more than 17,000 years old. Reconstructions of past local environments are also possible from the range of pollen and phytolith types identified. This approach should have widespread application to studies of rock-art dating and late Quaternary environmental change on continents where mud-wasps once Lived and other sources of palaeoecological information are absent.