We have 2 Cottage style house with a single tube size hole on a door that slides up and door on grooves from the upper right at about a 45 degree angle.
Yesterday I found bark dust piled at the bottom of the ‘V’ where the door stops. As I slid the door up there was more dust inside along with what looked like cotton.
These are 6′ off the ground. I cleaned them out.
This morning there is more cotton inside. I did see a small yellow jacket carrying cotton like material on the mason bee structure. After cleaning it out several times and perhaps because the weather has become cooler the cotton is no longer showing up inside. I actually saw a yellow jacket carrying a tuft of cotton like material. Please let me know if I should bring the two houses into the garage until it the yellow jackets are gone for the year.
Great pictures. I am not too sure who the culprit is here. Several mason beekeepers have sent me pictures with cotton in and around nesting tunnels. We are still searching for the culprit!
Taking the whole nest in is always good management.