Eudonia hemicycla is a moth in the Crambidae family. It was described by Meyrick in 1885. It is found in New Zealand. The wingspan is about 17 mm. The forewings are fuscous, with scattered pale ochreous-yellowish scales. There is a cloudy blackish spot on the inner margin near the base. Above this is a line of whitish scales. The hindwings are fuscous-grey, becoming dark fuscous towards the hindmargin. Adults have been recorded on wing in January.