Thetidia smaragdaria
In 3 days ~10% in a week ~30%
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. 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. In 2004 the moth was first recorded from Sweden.
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. Wikipedia →
| # | Park | Country | Daily sighting probability |
|---|---|---|---|
| 1 | Aigüestortes National Park | 🇪🇸 Spain | |
| 2 | Pyrénées National Park | 🇫🇷 France | |
| 3 | Sierra de Guadarrama National Park | 🇪🇸 Spain |
Rare
Under 5% of wildlife watchers report an Essex Emerald sighting in Sierra de Guadarrama National Park on a given day, based on 8 verified sightings from GBIF citizen-science data from 2019 to 2026. It is the 416th most-seen of the 597 insects we can rate there. Over three days the chance rises to about 10%, and over a week to about 30%, if each day is a fresh chance.
June and July
In those months about 10% of wildlife watchers report an Essex Emerald in Sierra de Guadarrama National Park on a given day, against under 5% in August to May, the lowest months. Those are among Sierra de Guadarrama National Park's driest months, with about 45 mm of rain a month against 110 mm in November.
Between 4 and 7 am
Across all the parks we cover, that three-hour window holds the most Essex Emerald sightings with a recorded time, and about 7 in 10 of them come between 6 pm and 6 am: it is most active around dawn and dusk.
3rd of 3
Of the 3 parks where we can rate Essex Emerald sightings, Sierra de Guadarrama National Park ranks 3rd at under 5%. The best odds are in Aigüestortes National Park (Spain, about 10%) and Pyrénées National Park (France, under 5%).
Same family: Geometridae
The closest relatives of the Essex Emerald that you can see in Sierra de Guadarrama National Park (family Geometridae, Geometer Moths) are Yellow Shell Moth (about 10%), Heliothea discoidaria (about 10%) and Chimney-Sweeper (about 10%), with each one's daily chance of a sighting.
GBIF citizen-science records
It is estimated from how often the Essex Emerald is recorded against all the insects logged in Sierra de Guadarrama National Park (8 verified sightings from 2019 to 2026), calibrated against known sighting rates. Figures are rounded to the nearest 10% because citizen-science data supports honest approximations, not decimals, and months with records from fewer than five people show "—". How it works.
