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using the following references:
A taxonomic revision of the hilara maura group - Chvala
The Hilara species (Diptera, Empididae) of Switzerland - Chvala

I arrive at Hilara maura, the most common species, especially in May.

https://www.flickr.com/photos/149164524@N06/34225516006/in/photostream/

Thank You for your time.