Icosidesmus worthingtoni is very widespread in Otago and is one species that is most tolerant of large differences in the natural covering vegetation and habitat but intolerant of any changes to the environment cased by humans. So far it has been found in the dense Nothofagus forests immediately west of Queenstown (rainfall ca 2- 3000mm) eastwards into the dry tussocky shrublands of Central Otago valleys (rainfall 400 mm) up to relatively high altitudes (900 m) in the adjacent mountains that are subject to much snow in winter and intense frosts before and after the snows. It is in coastal broadleaf forest at Moeraki and the wet, almost boggy broadleaf remnant forest at Edendale, Southland.