Sunday morning there were bees flying all over the field unusually, and on checking the hives, I found alot of bees crawling around and piling up all over one hive. I've not much experience (5 months, first 2 new packages this spring), but it was clear we were getting robbed. There was frenzied behavior and dead bees and fighting. We reduced the entrances of the two hives, and covered them with wet sheets. Sunday night we removed the sheets and shook off the bees, as we did not know if we had locked some robbers in, then replaced the sheets before the bees were up the next (Monday) morning. Bees were flying all around the hives all day yesterday (Monday) and we left the sheets on overnight. This morning there are many bees again, but I'm not sure how to tell if they are our bees at this point, and whether it's safe to remove the sheets. Thank you for any advice.