Synemon theresa, the cryptic sun-moth, is a species of day-flying moth of the family Castniidae. It was described by Edward Doubleday in 1846. It has a wingspan of 26-40mm, and is mostly grey-brown with orange hindwings. Native to Australia, this species is extinct in Victoria, and is now only known from a relatively small area of South Australia near Adelaide. It uses Themeda triandra (Kangaroo Grass) and Rytidopserma spp. (Wallaby Grasses) as larval food plants. Adults can be found from November to February. They only live for a few days, as they do not have a feeding proboscis. Despite becoming extinct over much of its former range, the cryptic sun-moth is not listed as a threatened species in South Australia.