Sialis lutaria
In 3 days ~20% in a week ~40%
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 Brussels, so these are its closest relatives here: other insects.
With luck
About 10% of wildlife watchers report a Common Alderfly sighting in Brussels on a given day, based on 15 verified sightings from GBIF citizen-science data. It is the 144th most-seen of the 337 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.
April
In that month about 20% of wildlife watchers report a Common Alderfly in Brussels on a given day, against under 5% in May to February, the lowest months. That is one of Brussels's driest months, with about 40 mm of rain against 80 mm in August.
Yes
Of the 3 cities where we can rate Common Alderfly sightings, Brussels has the highest daily chance: about 10%. Next come Paris (France, under 5%) and London (United Kingdom, under 5%).
GBIF citizen-science records
It is estimated from how often the Common Alderfly is recorded against all the insects logged in Brussels (15 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.
