Eudonia hemiplaca is a moth in the Crambidae family. It was described by Meyrick in 1899. It is found in New Zealand. The wingspan is about 18 mm. The forewings are dark fuscous with purplish reflections. There is an obscure line on the lower half which is slightly paler than the ground-colour, as well as a suboblong white blotch which is sprinkled with fuscous and margined by black suffusion. There is second line, which is also slightly paler than the ground-colour. This line is darker-margined and forms a whitish dot on the costa. The hindwings are pale grey with indications of a faint paler postmedian line.