I have seen around 3-4 individuals flying around at the same time.
Other times I have seen other black wasps with a very long ovipositor, but those looked a bit different with slightly longer bodies, I assumed those are parasitic wasps, I can't recall those trying to actually get inside the substrate like these ones.
The things can be lay larvae in Sempervivum are some hoverflies that lay inside the leaves and the vine weevil that lays inside the root system. But I have not seen the signs of those being present.
