Alors, je vous livre les réponses successives 1 à 3 :
1 - à ma demande initiale d'identification :
Indeed an interesting find, but considering you live in the richest part of France this is hardly a surprise.
It is at least a Mesitius species, and most likely Mesitius ruficollis. The raised pad between the antennal sockets is an exclusive marking for this genus. Some 40 years ago many more species were named Mesitius, but most of these were transferred to Heterocoelia. In fact I just recently started looking at Mesitiinae. They don't live in these parts of Europe, but I was asked to make a European key to the genera.
All Mesitiinae live in ants nests, and their coulour certainly reminds of red ants. They don't harm the ants but are parasitoids of coleopteran guests of the ants. Much more of the biology is not known.
2 - à ma question sur son sexe :
3 - à ma remarque sur le fait que cette liste (trouvée par une recherche avec "Mesitius ruficollis") connaît Heterocoelia ruficollis mais pas Mesitius ruficollis ; et que FE ne connaît aucun des deux binômes :Oh, yes… I forgot to mention. It's a female. Male bethylids are usually not micropterous, except for some minute Cephalonomia species.
You're right Pierre, I'll change this in my concept key.
The problem is in the tree publications on Mesitiinae by Móczár. My own key was based on Móczár's first publication on Mesitiinae in 1969. There he keys out Mesitius by having a 'spoon-like' clypeal carina. In the third issue (1971) however, he inserts a new key at the end of the paper, now proposing the same feature as unique for Heterocoelia.
As I said, I'm just starting with this subfamily. Some genera are so minimally described that I can't understand what the authors mean.
As for the species you may help me decide what it might have been. These are the couplets that remain in Móczár 1971:
12 Head black, pronotum red, mesonotum-scutellum brownish. Clypeus protruding in a triangle, raised into a high longitudinal keel. Costa of fore wings absent. Punctures of head not so deep and distinct as in foenarius Nagy. Head elongate. Frontal furrow distinct. Eye as long as its distance from occiput. 4.5 —5.7 mm. ruficollis (Kieffer)
– Mesonotum dark red in the middle and blackish on margins. Anterior margin of clypeus protruding in an oblong shape in the middle, gradually raising into n longitudinal sharp keel. Costa of fore wings present. Ocelli only with a slight deepening at outer margin, base of scutellum flat. Wings short. Half breadth of propodeal disc only slightly broader than length of propodeum. Eye separated from mandible by four-fifths length of an eye. 6 mm. foenaria (Nagy)