A juvenile plague skink (top) and a juvenile copper skink (bottom).
It can be very difficult to tell the difference between plague skinks and various New Zealand native skinks. Juveniles are especially difficult to distinguish. The best way is to look for the front-parietal head scale under a magnifying glass: single diamond-shaped in a plague skink and two scales in the same position in native skinks.
Photograph: by Dylan van Winkel