This is my first post. Thanks for all the good info. I have four hives and they are all being robbed. I used open feeders and even though they were about a hundred yards from the hives it happened. I built robber screens at least I think I did and installed them last night. The hives are calmer today and bees are leaving but I haven't seen a single bee find her way back in. I have an entrance at top about 3/4 inch but wonder if I should remove the whole top piece. Robbing was pretty bad but now I'm worried they may not be able to get back in. Thanks!