Sialis fuliginosa


One of three similar species of Alder fly.

Identification difficulty
Recording advice

There are three very similar Sialis species in Britain and detailed examination is required for species identification. When submitting a record for Sialis species please mention the details that you have used to help you to determine the species.  Any records without this information can only be accepted as 'Plausible'.  In order to distinguish the three species of Sialis, examination of the external genitalia (males) or anal plates (females) is required, but is relatively easy as no dissection is required.


Sialis fuliginosa seems to be restricted to areas with flowing water.

When to see it

Peak time is May and June.

Life History

The adults only last long enough to mate and deposit eggs which are laid in large masses on vegetation near to water. After hatching the larva fall into the water where they predate on other small invertebrates. Pupation takes place in debris by the water’s edge after 12 to 24 months, with the adults emerging a few weeks later.

UK Status

Widespread in Britain but less common and more local than Sialis lutaria.

VC55 Status

It seems to be infrequent or under recorded in Leicestershire and Rutland.

Leicestershire & Rutland Map


Yellow squares = NBN records (all known data)
Coloured circles = NatureSpot records: 2020+ | 2015-2019 | pre-2015

UK Map