Thecla betulae
In 3 days ~10% in a week ~20%
The brown hairstreak (Thecla betulae) is a butterfly in the family Lycaenidae. The range includes most of the Palaearctic. The following description of this butterfly was written by Adalbert Seitz in 1909: Z. betulae L. Black-brown; male with a pale diffuse patch, female with a broad orange band beyond the crossveins. Underside ochreous, with dark-edged white lines. In North and Central Europe und Northern Asia eastward to the Pacific. Tutt name males without the pale diffuse patch beyond the crossveins ab. unicolor, while this patch is nearly white in ab. pallida Tutt. In ab. spinosae Gerh. there appear beyond the apex of the cell small orange-spots, which may be paler yellow than the discal spots of the female. The orange discal band of the female is sometimes narrow: ab. restricta Tutt, and sometimes broad (= ab. lata).
females in which the band is pale ochreous instead of orange are ab. fisoni Wheeler, while the band is separated into several spots by the heavily black veins in ab. lineata Tutt. A very remarkable form is ab. cuneata Tutt, which bears a broad orange submarginal band on the hindwing. On the underside the white lines are sometimes more or less... Wikipedia →
| # | Park | Country | Daily sighting probability |
|---|---|---|---|
| 1 | Cévennes National Park | 🇫🇷 France | |
| 2 | Bavarian Forest National Park | 🇩🇪 Germany |
Rare
Under 5% of wildlife watchers report a Brown Hairstreak sighting in Vienna on a given day, based on 12 verified sightings from GBIF citizen-science data. It is the 895th most-seen of the 1406 insects we can rate there. Over three days the chance rises to about 10%, and over a week to about 20%, if each day is a fresh chance.
August
In that month about 10% of wildlife watchers report a Brown Hairstreak in Vienna on a given day, against under 5% in September to July, the lowest months. That is one of Vienna's wettest months, with about 85 mm of rain against 40 mm in February.
Between 2 and 5 pm
Across all the parks we cover, that three-hour window holds the most Brown Hairstreak sightings with a recorded time, and about 9 in 10 of them come between 6 am and 6 pm: it is a daytime animal.
10th of 11
Of the 11 cities where we can rate Brown Hairstreak sightings, Vienna ranks 10th at under 5%. The best odds are in London (United Kingdom, about 10%), Prague (Czechia, about 10%) and Munich (Germany, about 10%).
Same family: Lycaenidae
The closest relatives of the Brown Hairstreak that you can see in Vienna (family Lycaenidae, Gossamer-winged Butterflies) are Common Blue (about 20%), Sooty Copper (about 10%) and Holly Blue (about 10%), with each one's daily chance of a sighting.
GBIF citizen-science records
It is estimated from how often the Brown Hairstreak is recorded against all the insects logged in Vienna (12 verified sightings), 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.
