When I noticed that the wasps were using water from the hummingbird feeder, I
set out to change the color. I removed the feeder and replaced it with a small dish
filled with water colored with green food color, and it worked. Large green drops
of water are at the opening cells with grubs in them. I guess that the water is for
the grubs to drink!! I placed similar green water dishes near other wasp nest but
had no success.