Geomyza tripunctata

Quite a distinctive fly apparently, and evidently very common. Geomyza majuscula has a fairly similar wing pattern (but lacking the clouding at the base). The key also draws attention to differences in the setae on the anepimeron and the shape of sternite 8 on the female terminalia. The smaller setae were hard to see but both flies showed one strong seta on the anepimeron which should be lacking on majuscula. Sternite 8 seemed to be slightly notched on both which is not quite as described and illustrated in the key (entire in tripunctata) but even more unlike that described and illustrated for majuscula (it more closely resembles the illustration for venusta but the wing pattern rules that out).

female Geomyza tripunctata showing anepimeron and sternite 8, Wendling Beck Environment Project (Norfolk, UK), 18th November 2022

second female Geomyza tripunctata showing anepimeron, Wendling Beck Environment Project (Norfolk, UK), 18th November 2022

female Geomyza tripunctata showing anepimeron, base of wing and ovipositor, Wendling Beck Environment Project (Norfolk, UK), 3rd August 2023

These two were both found by suction sampling. When I first examined them the abdomen tips looked so different from one another that I thought I must have one of both sexes. On closer inspection I couldn't see what I was looking for in a male and the bit sticking out looked suspiciously like a female ovipositor - they were in fact both females but one had the tip more fully withdrawn into the abdomen. Sternite 8 was not externally visible at all in this one so I dissected it for a clearer look. I then did the same for the other one as I realised it made it much easier to view sternite 8. Interestingly one was clearly notched and the other was rounded. Some variation in the shape is consistent with the key althought it doesn't illustrate or describe such a notch.

female Geomyza tripunctata showing wing, anepimeron, abdomen tip (ventral and lateral views) and sternite 8, Wendling Beck Environment Project (Norfolk, UK), 12th March 2025

second female Geomyza tripunctata showing wing, anepimeron, abdomen tip and sternite 8 with ovipositor, Wendling Beck Environment Project (Norfolk, UK), 12th March 2025