There are three species of megalopteran in the British Isles: Sialis lutaria, Sialis fuliginosa, and Sialis nigripes. These species can only be identified from examining their genitalia, the identification features are shown below for both Male and Female specimens.
![](https://www.laars.jamesjepson.com/wp-content/uploads/2023/11/MegspeciesID-1024x746.png)