Essex emerald

The Essex emerald (Thetidia smaragdaria) is a moth of the family Geometridae. The species was first described by Johan Christian Fabricius in 1787 as Phalaena smaragdaria.[1] It is distributed throughout the Palearctic region with records from many European countries. The British subspecies Thetidia smaragdaria maritima was last seen in 1991 in Kent and is now presumed extinct.[2] In 2004 the moth was first recorded from Sweden.

Illustration from John Curtis's British Entomology Volume 6

Essex emerald
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Lepidoptera
Family:	Geometridae
Subfamily:	Geometrinae
Tribe:	Comibaenini
Genus:	Thetidia
Species:	T. smaragdaria
Binomial name
Thetidia smaragdaria (Fabricius, 1787)
Synonyms
Phalaena smaragdaria Fabricius, 1787 Phorodesma castiliaria Staudinger, 1892 Euchloris maritima Prout, 1935 Geometra prasinaria Eversmann, 1837 Geometra gigantea Milliere, 1874 Geometra volgaria Guenee, 1858

The wingspan is 27–35 mm. There is one generation per year with adults on wing from mid-June to mid-July.

The larvae feed on Artemisia maritima and Achillea millefolium. Larvae can be found from July to June the following year. It overwinters in the larval stage.