There are 13 species of Hemerobius in the British Isles. To decide which species you have you first of all need to look at the crossvein MCCV and the forewing patterns. If the MCCV is colourless (or if dark, the membrane around is clear) and there is no strong forewing pattern click here. If MCCV is dark (with membrane dark around crossvein) and the forewing has a clearly visible pattern, click here.
There are two species that have a colourless MCCV (or if dark, the membrane around is clear) and no forewing colour pattern: Hemerobius nitidulus and H. micans. These two species can be distinguished from one another by looking at the pattern on the longitudinal veins (see image below).
There are 10 species in the British Isles that have a dark MCCV (with dark coloured membrane around) and a visible colour pattern on the forewing. To start to differentiate between these species, first of all look whether there is a pale thoracic stripe (see below image), if there is no stripe then you have Hemerobius stigma (click here), if there is click here.
Hemerobius stigma
Hemerobius stigma can be identified by not having a pale thoracic stripe, the wing membrane has some shading, and there is an orange coloured pterostigma (see below image).
The species that have a pale thoracic stripe can be further differentiated by face colour, if the face is a shiny glossy black colour, then you have Hemerobius atrifrons (click here), if the face is brown and not shiny, click here.
Hemerobius atrifrons
The black glossy shiny face is a distinctive character for this species (see image below).
The species with a non-glossy brown face can be further divided by the basal SCRCV crossvein. If it is pale or only slightly darkened at the end that joins R, this gives Hemerobius marginatus or H. lutescens (click here), if it is dark (usually black), click here.
Hemerobius marginatus and H. lutescens can be differentiated based on the width of the costal area, colour pattern of forewing, and the male genitalia.
The species with the dark SCRCV can be diffferentiated by the shading on the hind margin of the forewing (see image below). If there is uniform shading click here, if there are transparent areas click here.
There are three species with uniform shading, Hemerobius striatus, H. contumax and H. pini. To differentiate between these species, first look at the gradate series of crossveins (see below image). If the inner series is dark and the outer is pale you have Hemerobius striatus (click here), if both inner and outer are dark click here.
Hemerobius striatus
The defining features are given in the image below.
The two species with the dark inner and outer gradate series of crossveins, Hemerobius contumax and H. pini, can be differentiated by the angles of the gradate series (see below image). In Hemerobius contumax they are close and parallel, in H. pini they are diverging and not parallel. If you identify your insect as Hemerobius contumax please retain the specimen and contact the recording scheme for verification, as this species was last recorded in 1952.
There are three species that do not have uniform shading along the hind margin of the forewing, these are Hemerobius simulans, H. perelegans and H. humulinus.
To start to differentiate these species you need to look at the gradate series of crossveins, size of the transparent areas, wingspan, and the scape (see image below). If the inner series is in a straight line, the transparent areas are small, wingspan greater than 20 mm, and the scape (usually) has a dark stripe, you have Hemerobius simulans (click here), if not you have either H. perelegans or H. humulinus (click here).
Hemerobius simulans
Identified from the features in the below image.
To differentiate between Hemerobius perelegans and H. humulinus you need to look at the patterns on the veins and wing membrane, and the overall colour of the wings (see below image).
