Plague skink with kill, showing distingishing single scale on the head.
Plague skinks have one large scale on the top of their head, whereas New Zealand native skinks have two smaller scales. The single diamond-shaped fronto-parietal head scale is located on top of the head, directly between the eye sockets.
See the 'other clues' section on this plague skink page for a comparative diagram.
Photograph: by Linda Coster (cropped from original)