Ennomos erosaria
In 3 days ~20% in a week ~40%
Ennomos erosaria, the September thorn, is a moth of the family Geometridae. The species can be found in the Palearctic realm in western Europe and from central Scandinavia. Its range extends to the northern Mediterranean and east to the Caucasus and Russia.
It is widespread in mixed and deciduous forests in Europe. The south eastern occurrence reaches Turkey and the Caucasus. The main habitat is dry deciduous forests and parks. In the Southern Alps, the species rises to an altitude of about 1600 metres.
The wingspan is 30–35 mm. The length of the forewings is 17–21 mm. The ground colour is straw yellow to ochre-yellow. The colour is darker on hindwing termen and the hindwing also has a faint discal spot. The fasciae (bands) are brown. The inward arc under projection on distal forewing is prominent. The name typical form is yellowish. ab. tiliaria Hbn. is paler, the forewing straw-colour. — ab. tinicoloria Esp. is without the transverse lines.
Similar species: other Ennomos species. The moths fly in one generation from July to October.[1] They are attracted to light. The larva which is rather elongate, with strong knob-shaped protuberances, altogether bearing a remarkable likeness to an oak twig is brown, now with
a tinge of purple, now of greenish, the ventral surface paler greenish brown. It feeds on oak, birch, and lime. Wikipedia →
| # | Park | Country | Daily sighting probability |
|---|---|---|---|
| 1 | Snowdonia National Park | 🇬🇧 United Kingdom | |
| 2 | Bavarian Forest National Park | 🇩🇪 Germany | |
| 3 | Sierra de Guadarrama National Park | 🇪🇸 Spain |
With luck
About 10% of wildlife watchers report a September Thorn sighting in Bavarian Forest National Park on a given day, based on 11 verified sightings from GBIF citizen-science data from 2019 to 2026. It is the 471st most-seen of the 1115 insects we can rate there. Over three days the chance rises to about 20%, and over a week to about 40%, if each day is a fresh chance.
June and August–September
In those months about 10% of wildlife watchers report a September Thorn in Bavarian Forest National Park on a given day, against under 5% in July and October–May, the lowest months.
Between 8 and 11 am
Across all the parks we cover, that three-hour window holds the most September Thorn sightings with a recorded time, and about 6 in 10 of them come between 6 am and 6 pm: it is seen both by day and at night.
Among the best
Of the 3 parks where we can rate September Thorn sightings, Bavarian Forest National Park ranks 2nd at about 10%, level with the leaders once rounded. The best odds are in Snowdonia National Park (United Kingdom, about 10%).
Same genus: Ennomos
The closest relatives of the September Thorn that you can see in Bavarian Forest National Park (genus Ennomos) are Dusky Thorn (about 10%) and August Thorn (about 10%), with each one's daily chance of a sighting.
GBIF citizen-science records
It is estimated from how often the September Thorn is recorded against all the insects logged in Bavarian Forest National Park (11 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.
