As I was tagged, too ... :-)

On the other hand, the photo of the ant is not very good to identify ...

I agree.

... as it could be one of the species of that genus Monomorium.

Maybe. However, I think typical for most Monomorium species is an elongated structure with two humps just before the abdomen begins, and I cannot spot that in the picture ...

It may be helpful to know where (which country?) these ants have been found but might still not be easy to identify their genus (or even exact species) having just that single photo.