There are two species of Semidalis in the British Isles:
Semidalis aleyrodiformis and Semidalis pseudouncinata
Both these species share the following features.
![](https://www.laars.jamesjepson.com/wp-content/uploads/2024/01/Semidalis-1024x681.jpg)
To identify the individual species of the genus you need to examine the male genitalia, in particular the shape of the parameres (see image below).
![](https://www.laars.jamesjepson.com/wp-content/uploads/2024/01/Semidalis-spp-1024x768.jpg)