Micromus angulatus

Micromus angulatus is described in Plant (1997} as widespread but usually scarce and local in England. Until 2024 there was only one Norfolk record, from Santon Warren in the 1980s. Seven have been found at sites across both east and west Norfolk in 2024 (mostly late September to mid October).

Micromus species differ from most other brown lacewings in forewing detail, having no recurrent humeral vein and at least 3 branches to the radial vein. Of the 3 Micromus species, variegatus is distinctive in having a characteristic wing pattern. Micromus angulatus differs from the commoner paganus in having more rounded forewings, only four branches to the radial vein (but beware paganus can also have only four) and usually more reddish-brown forewings (more yellowish-brown in paganus). The tip of the males' abdomen is also quite different in paganus, but note that the specimens found in 2024 have also differed quite significantly from the diagram in Plant (1997).

This female was one of two that came to light the same night in my garden. Plant doesn't provide any information about the abdomen shape in females and I have not yet examined a female paganus, so I don't know if the abdomen differs between the two species in any way.

female Micromus angulatus showing wings (including close-up of base of forewing) and tip of abdomen (from side and below), North Elmham (Norfolk, UK), 16th October 2024

When I first looked at the adbomen on the live insect with a hand lens I couldn't see any projections and thought it was a female. When I later examined the specimen I was surprised to find that it was actually a male. The projecting elements of the abdomen had not been so obvious in life, but even examining the deceased specimen under the microscope they did not match the diagram in Plant's key. Plant describes a "small, narrow horizontal spike, suspended from the last segment". In this specimen there were in fact several projections from the tip of the abdomen. There was a pair of small narrow spikes emerging from just above the tip of the lower lip (the last sternite I think). These were slightly upturned and curved inwards so from below they crossed at the base and diverged strongly. A larger pair of projections above these emerged from the last tergite, angled diagonally downwards and narrowing abruptly at the tip where they were hooked inwards. Passing up between these, and emerging from between gap where the tergite and sternites join was a structure fairly straight but slightly upturned. It was pretty difficult to reconcile what I was seeing with the key. After clearing the abdomen in potassium hydroxide solution I could match part of the abdomen tip with Plant's diagram. You have to ignore the lower lip (I think that's the apical sternite) and some of the other bits, but what's illustrated in Plant is, I think, the apical tergite and one of the bits (parameres??) sticking out from it.

male Micromus angulatus showing wings (including close-up of base of forewing) and tip of abdomen (5 views before clearing and one side view after clearing), North Elmham (Norfolk, UK), 16th October 2024

The first of 2024's crop of angulatus that I became aware of was one found by James Emerson in Norwich city centre on 30th September. He shared a photo of the abdomen taken almost side on and there was no sign of any projection at all, and we thought it was a female. I subsequently examined the specimen and was surprised to find it was in fact a male. The projections were harder to see and were not so extruded as on mine, but they essentially had the same form. In perfect side view some were visible but I had to open up the gap between the last sternite and tergite to see all the projections that had been visible on mine above. As with mine, it was difficult to reconcile with the diagram and description in Plant, but it is very clearly different from the large downcurved claw on Micromus paganus.

abdomen of male Micromus angulatus, Norwich (Norfolk, UK), 30th September 2024 (found by James Emerson)