Lasius umbratus

The records in the NBN Atlas seem to be concentrated in the Brecks (so far as Norfolk is concerned) although there are a few others elsewhere. These will be submitted to the county recorder in due course, once I've pulled my other ant records together.

Routinely when keying ants one of my first struggles is determining whether the opening of the propodeal spiracle is elongate and on the side face of the propodeum (genus Formica) or nearly circular and on the curved surface between the side and hind faces of the propdoeum (Lasius). Sometimes this seems reasonably obvious, but sometimes it isn't - to me at least. On this one the opening was far enough away from the hind face of the propodeum for me to think it was on the side face (but in fact the corner was so broadly curved I think it was just about on it). The opening wasn't completely spherical, but much more so that some of the slits I've seen on Formica fusca.

I re-examined this after gaining experience with Lasius fuliginosus. I briefly toyed with the idea that this one could be another fuliginosus if I had been too strict in interpreting some brownish tones on the body as ruling out fuliginosus. But comparing the specimen side-by-side with the winged female fuliginosus there are a number of other differences. It's very nmuch smaller and it has erect hairs on the scape, femora, tibia and basitarsi that are lacking on the fuliginosus.

female Lasius umbratus showing propodeum, underside of hind tibia, abdominal hairlength compared to width of hind basitarsus and antenna, Wendling Beck Environment Project (Norfolk, UK), 29th October 2022

I don't have such detailed photos of my only previous record of this species, but I used the same key (Skinner and Allen) to identify it.

female Lasius umbratus, North Elmham Cathedral Meadows (Norfolk, UK), 9th August 2018