Sialis lutaria
In 3 days ~10% in a week ~20%
Sialis lutaria, common name alderfly, is a species of alderfly belonging to the order Megaloptera family Sialidae. This species is mainly present in Austria, Belgium, United Kingdom, Czech Republic, France, Germany, Italy, the Netherlands, Spain, Poland, Romania and Switzerland.
Adults of this species usually inhabits ponds and slow-flowing streams, while the larvae live in mud and detritus under water. Adults can reach 20 millimetres (0.79 in) of length, with a wingspan of 22–34 millimetres (0.87–1.34 in). They have a stocky body with a black or dark brown basic coloration, including head and legs. The wings are greyish, membranous and translucent, with pronounced dark venation. At rest they are held roof-like over their body.
The flat larvae reach approximately 17 millimetres (0.67 in). They have large heads, powerful jaws and three pairs of legs. Furthermore, they show feathery gills on the abdominal segments. The abdomen terminates with a long gill.
Adults are most often encountered from May through June on vegetation near slow-flowing streams or close to ponds. They are bad fliers and never leave the waters where... Wikipedia →
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More parks will be added in future updates.
No species of the same family or order lives in London, so these are its closest relatives here: other insects.
Rare
Under 5% of wildlife watchers report a Common Alderfly sighting in London on a given day, based on 8 verified sightings from GBIF citizen-science data. It is the 1219th 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 20%, if each day is a fresh chance.
Any time of year
In every month with enough records, under 5% of wildlife watchers report a Common Alderfly in London on a given day, so our monthly data shows no clear season.
3rd of 3
Of the 3 cities where we can rate Common Alderfly sightings, London ranks 3rd at under 5%. The best odds are in Brussels (Belgium, about 10%) and Paris (France, under 5%).
GBIF citizen-science records
It is estimated from how often the Common Alderfly is recorded against all the insects logged in London (8 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.
