haa haa
not borax but boric acid. They take it back to the nest.
I read they won't cross talcum powder. I use it on top of my flat hummingbird feeders. (not much wind here) It worked.
One day I saw them coming in my window, so I thought..Haa I will fix you little devils. I sprinkled talcum powder across the window sill. They just went up the wall and around the powder. oh well H$((.