Tachina magnicornis (?)

Until 2023 known in the UK only from the Channel Islands. A 2025 paper in Dipterists Digest* lists 37 records from between Cambridgeshire and Kent from 2023 to 2025. Of these two 2025 records are from the Norfolk Brecks, but I imagine that now awareness of the species is increasing, further Norfolk records from this period will come to light (e.g. I see from BlueSky that Andy Musgrove has had one at Shotesham).

* Basham, D., Raper, C. and Falk, S. 2025. Tachina (Eudoromyia) magnicornis (Zetterstedt) (Diptera, Tachinidae) new to Britain. Dipterists Digest 32, 162-167. Accessed here.

This came to light in my garden. I am not a dedicated dipterist and have only occasionally identified the very common Tachina fera, usually from photos not specimens. Apart from one male fera, I don't currently have access to any specimens of either species to compare this to. I am leaning towards calling this magnicornis but there are one or two problems that are causing me to hold back from claiming that with certainty.

I am not very experienced with sexing Tachina but on my male specimen of Tachina fera the genitalia are obvious, which they are not on this specimen, so I'm pretty sure this is a female. I think the length of the claws on the front tarsus also support it being a female and at least rule out male fera.

I think the following characters seem to point to magnicornis:

• The frons appears to be very wide. Some references provide ratios of frons width to eye width but it is not clear to me where I should take the measurements from, so I have not calculated this ratio. However from a visual comparison of my fly with photos of fera and magnicornis I think the frons is very wide on mine, as in magnicornis and too wide for any fera.
• The front and mid tarsi are very dark, except the basitarsus. Some references suggest that only the base of the basitarsus should be paler on magnicornis, whereas on this one most of the basistarsus is paler (only the apex is dark). Steven Falk's photos of magnicornis show darker basitarsi so this is a concern, especially as photos of fera tarsi show some variation in darkness. However, tarsal segments 2-5 are very dark so I think this fits magnicornis best.
• The dark longitudinal stripe through the top of the abdomen is narrow.
• The dusting on the parafascialia is silvery-white. The penultimate photo below shows how this contrasts with the more golden dusting on the face above this - I took care with this photo to ensure the lighting was as even as possible, and when examining the face under the microscope while varying the lighting, I could not detect any yellow or golden tones on the dusting of the parafascialia.

However, as well as the paler-than-expected fore basitarsus, the front femora are also paler than expected. These are supposed to dark at the apex on magnicornis whereas this was hardly the case here - they become a little darker towards the base, but they are almost entirely orange (the flattened face that rubs against the coxa is darker). This is my biggest concern leaving me in doubt as to its correct ID.

My understanding from Chris Raper's post here is that Tachina nupta is now synonymised with Tachina magnicornis, in which case the pointed end to the dorsal stripe (pointing to nupta rather than magnicornis in earlier work) and the fact that the fourth fore tarsal segment is only marginally wider than long (intermediate between nupta and magnicornis per earlier work) should not count against this being magnicornis.

For now, the orange front femur and basitarsi are leaving me in sufficient doubt about the ID that I won't record it as magnicornis until I either have confirmation from someone more experienced (if you can help, please shout) or else until I've been able to compare to more specimens including female fera.

probable female Tachina magnicornis showing frons/head (3 angles), front and mid tarsi, front tarsus, front tarsomere 4 (on both legs), front femur, parafacialia and tip of abdomen from below, North Elmham (Norfolk, UK), 3rd October 2025