Acentria ephemerella
In 3 days ~20% in a week ~30%
Acentria is a monotypic genus of moth of the family Crambidae that was described by James Francis Stephens in 1829. Its only species, Acentria ephemerella, the watermilfoil moth or water veneer, was described by Michael Denis and Ignaz Schiffermüller in 1775. It is used as an agent of biological pest control against the noxious aquatic plant known as Eurasian watermilfoil (Myriophyllum spicatum).
The adult male is a white moth with a wingspan of about 12 millimeters. Forewings whitish, veins and costa obscurely brownish. Hindwings whitish. Wings in female often rudimentary, but sometimes larger than in male, up to 23 mm. Larva light olive-green; head light brown.
The development of the wings of the female appears to vary considerably, but under what circumstances is still uncertain. There are two female morphologies. Most females are flightless and live on the surface of the water or just submersed. A few females have longer wings and fly. This is an aquatic insect; most of its life cycle takes place in the water. The female is fertilized at the surface and dives to lay egg masses on aquatic plants, such as Potamogeton spp., Canadian waterweed Elodea canadensis and watermilfoil. The larva emerges and bores into the stem of the plant, gluing together plant material to create a shelter. It girdles stems as it feeds, which causes significant damage to the plant as stems and leaves die or break off. The larva pupates inside an underwater cocoon filled with air. Upon emergence, males and flighted females swim to the water surface and fly away.
This moth is used as a biocontrol agent on watermilfoil, but carefully, because it lacks host specificity and will attack other plant species, including natives. It tends to prefer M. spicatum over other plants. This is a European moth, but it was found in Canada in the 1920s, having been probably introduced accidentally. It is established in much of the northeastern United States, where it appears to have the ability to reduce watermilfoil infestations. Wikipedia →
| # | Park | Country | Daily sighting probability |
|---|---|---|---|
| 1 | Wadden Sea National Park | 🇩🇪 Germany |
More parks will be added in future updates.
| # | City | Country | Daily sighting probability |
|---|---|---|---|
| 1 | Liverpool | 🇬🇧 United Kingdom | |
| 2 | London | 🇬🇧 United Kingdom | |
| 3 | Birmingham | 🇬🇧 United Kingdom | |
| 4 | New York City | 🇺🇸 United States |
With luck
About 10% of wildlife watchers report a Water Veneer sighting in London on a given day, based on 53 verified sightings from GBIF citizen-science data. It is the 457th most-seen of the 1504 insects we can rate there. Over three days the chance rises to about 20%, and over a week to about 30%, if each day is a fresh chance.
June to August
In those months about 10% of wildlife watchers report a Water Veneer in London on a given day, against under 5% in September to May, the lowest months.
Between 10 pm and 1 am
Across all the parks we cover, that three-hour window holds the most Water Veneer sightings with a recorded time, and about 7 in 10 of them come between 6 pm and 6 am: it is seen both by day and at night.
Among the best
Of the 4 cities where we can rate Water Veneer sightings, London ranks 2nd at about 10%, level with the leaders once rounded. The best odds are in Liverpool (United Kingdom, about 10%).
Same family: Crambidae
The closest relatives of the Water Veneer that you can see in London (family Crambidae, Crambid Snout Moths) are Box Tree Moth (about 30%), Mint Moth (about 20%) and Garden Grass-Veneer (about 20%), with each one's daily chance of a sighting.
GBIF citizen-science records
It is estimated from how often the Water Veneer is recorded against all the insects logged in London (53 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.
