Aplocera plagiata
In 3 days ~10% in a week ~30%
Aplocera plagiata, known as the treble-bar or St. John's wort inchworm, is a moth of the family Geometridae. The species was first described by Carl Linnaeus in his 1758 10th edition of Systema Naturae. It is found throughout the Palearctic region and the Near East.
This species varies considerably in size (wingspan 37–43 mm) and colouration, but is generally grey with three characteristic dark fascia across each forewing, that resemble a musical 'Staff', giving it its common name. The hindwings are pale grey or buff. Many forma have been described. (See Prout's The Macrolepidoptera of the world)
Aplocera plagiata is difficult to certainly distinguish from its congener Aplocera efformata (See Townsend et al.) One or two broods are produced each year. In the British Isles, the adults can be seen at any time from May to September. The species flies at night and is attracted to light.
The egg is whitish, without gloss, micropylar rosette 11- to 12-leaved, the sides with regular polygonal reticulation, each cell again more irregularly subdivided. The larva is also very variable, being green to reddish brown with alternating darker and lighter stripes. It feeds on various species of St John's wort (Hypericum species). It overwinters as a small larva. Wikipedia →
| # | Park | Country | Daily sighting probability |
|---|---|---|---|
| 1 | Snowdonia National Park | 🇬🇧 United Kingdom | |
| 2 | Bavarian Forest National Park | 🇩🇪 Germany | |
| 3 | Cévennes National Park | 🇫🇷 France | |
| 4 | Pyrénées National Park | 🇫🇷 France |
Rare
Under 5% of wildlife watchers report a Treble Bar sighting in London on a given day, based on 32 verified sightings from GBIF citizen-science data. It is the 593rd most-seen of the 1504 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.
May and August–September
In those months about 10% of wildlife watchers report a Treble Bar in London on a given day, against under 5% in June–July and October–April, the lowest months.
Between 6 and 9 am
Across all the parks we cover, that three-hour window holds the most Treble Bar sightings with a recorded time, and about 7 in 10 of them come between 6 am and 6 pm: it is a daytime animal.
3rd of 6
Of the 6 cities where we can rate Treble Bar sightings, London ranks 3rd at under 5%. The best odds are in Kharkiv (Ukraine, about 10%) and Prague (Czechia, about 10%).
GBIF citizen-science records
It is estimated from how often the Treble Bar is recorded against all the insects logged in London (32 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.
