Only have one hive with a screened bottom board. Pulled it the other day to clean it off and found this?(http://uploads.tapatalk-cdn.com/20160827/146b3391915407d2a23c5b00bb034089.jpg)(http://uploads.tapatalk-cdn.com/20160827/b4fd89aae526eb2b9ae025ef03c420f9.jpg)
Looks like grass seeds. Do you have mouse guards on your hives. Mice will nest in bottom of hives. They will destroy a hive. Squeeze a seed just to check it. If it is seeds that's what you got going on.
John
Pretty warm out yet for mice. Have had one or two in the fall before. Don't see any droppings. But haven't looked for a mouse.
Do you have wheat fields near by or do you have stored wheat. Looks like some of it is wheat.
Jim
I see mouse droppings in with the seeds when I zoom in on your photos.
So do I.
Last year we found a mouse nest in early August in one of the hives of my friend.
Break down that hive, clean out the mouse mess and put a guard on it. Might as well pt mouse guards on the others as well.