Well the mason bees I set free have been hanging around the yard. They're so timid and curious. I swear one even recognized me. It flew around me in a curious manner. I'm still not sure releasing them was the right thing to do now that I know they're an invasive species. We have an awful lot of mason bee species in the US and they're so friendly too. The only way I could see one of them becoming invasive is if they hatched out earlier than all the rest to get prime hole reinstate for a nest. Perhaps parasitic wasps and sawflies don't use them as hosts or are somehow overlooked by woodpeckers which would eat the natives. I haven't found a clear answer yet.