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Something like Meigenia or Vibrissina?
( the latter suggested by Waldgeist on iNaturalist... comparable to
https://diptera.info/forum/viewthread.php?thread_id=115974 )

Only 3-4mm or so in size.
Malvern Hills, UK
11/08/25

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I think, female Vibrissina turrita is correct.

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Interesting. Thanks!
We only have Vibrissina debilitata on the UK list according to NBN :
https://species.nbnatlas.org/species/NBNSYS0000138850#classification

How do you delineate between the two?

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Firstly - it looks very much like the one I saw ovipositing on larvae of it's host Arge pagana - see: https://diptera.i..._id=107515

I compared with T&H and Ceretti:
V. turrita:
Tergites 3 and 4 with broad, more or less regular pruinose basal bands over 3/5-4/5 of the length;
the slight longitudinal discontinuity along the middorsal edge shows a thin black band
that often disappears depending on the angle of incidence of the light.

V. debilitata:
Tergites 3 and 4 with pruinose basal bands, sparsely dense dorsally and extending over 1/3-1/2 of the length of the segment, while laterally they are denser and slightly more extensive;
very pronounced middorsal dark band, about half the width of the distance between the midmarginal setae.

My mistake: I didn't check whether V. turrita is listed for the UK, sorry!

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Ok nice, thanks!

I'm not sure I see a clear delineation in the photos based on the information from the key though - did you add those parts in bold because you see that as being diagnostic in these images and that it should indeed point to V.debilitata ...or...?

For me,
I would say the thin black band appears to disappear in some images.
I would also say that the pruinose basal bands are over 3/5-4/5 of the length (?)
But maybe I am misinterpreting the text.

Fwiw, further images can be seen here :
https://www.inatu.../305615689

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I think we will not succeed with the pruinosity and the central band of the abdomen!

There are 2 more characteristics in the key:
female turrita:
- Postpedicel 3.9-4.5 times as long as pedicel.
- Facial edge with setae over 1/2-4/5 of the length.

female debilitata:
- Postpedicel 2.9-3.6 times as long as pedicel.
- Facial edge with setae along 2/5-3/5 of the length.

I've seen your images at inaturalist and now I'm quite sure that the antenna is conformably with the definition in the key for debilitata and distinctly smaller than turrita's!

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Nice. Yes, agreed - seems correct to me too :)
Thanks!

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I am sorry to disagree, the abdominal patttern is way off. Moreover, there are erect scutellar bristles. So, to me, female Meigenia


Thro

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Thanks a lot once more for the salvation, Theo!

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Haha, ok good to know...that's what I expected originally.
Less exciting...but thanks!