Thalera fimbrialis, the Sussex emerald, is a species of moth of the family Geometridae, found in Europe and across the Palearctic to the area surrounding the Amur River in China.

Larva overwinter part-grown and when fully grown is long and thin, green with a brownish-red dorsal stripe that is sometimes broken up into a variety of spots.

It is a Red Data Book species in the UK, only breeding in the Dungeness area of Kent and one site in Rye, East Sussex.

[6] First described by Giovanni Antonio Scopoli, in his Entomologia Carniolica, published in Vienna in 1763; he named the moth Phalaena fimbrialis.

It was later places in the genus Thalera, from thaleros i.e. blooming, fresh, youthful – from the spring-like, green colour of the wings.