Robbing Behavior, Prevention and Treatment

Just like all other creatures on the planet, honey bees will also take advantage of ways to easily get their next meal, especially when there is no food in the field, such as nectar producing flowers. Bees will rob from other hives when there is no nectar flow, in cases where a hive is vulnerable, weak or queenless. All of those things can be helped by good beekeeping. When the first taste of fall is in the air you should close your hives down so that they have a smaller area to defend against robbing bees, hornets and wasps. This would address a hive's vulnerability. This also helps hives that are weak more efficiently defend their hive. Queenless hives can be given a queen, queen cell, or even a frame of eggs to allow them to raise another queen. However, if drones have already been kicked out of the hive you will have to settle for purchasing a mated queen or uniting with a queen right hive.
In many cases, the beekeeper is responsible for creating a situation where honey bees focus on robbing. Placing a common syrup can, wet honey supers, capping, etc. in order for the bees to "clean up" create a situation where the bees become prone to robbing. Just this act alone creates a situation where honeybees from many different hives (both yours and others) come into close proximity which causes disease transmission, varroa mite transfer between hives and overall aggressive behavior from honey bees. This contributes to the problem of CCD. Also, it is a misnomer that setting out "feed" (i.e. cappings or wet honey supers, sugar syrup) will allow hives that are light with honey going into winter to gain more weight. In fact, strong hives become heavier and lighter, weaker hives become weaker. Once the "feed" is gone, strong hives will turn their attention to weak hives and start robbing them!
Hives that are being robbed, depending on the severity, will become very defensive and will sting more readily, become weaker because of the battle going on at the entrance and if left unchecked will eventually perish. If the entire yard has been frenzied into robbing, the entire yard will become defensive.
Putting out common feed for bees also attracts wasps and hornets, beetles and wax moths, mice, skunks, etc. This can also contribute to hives dying in the winter months because these other insects will also start to rob from your hives.
Prevention of robbing is key. First, don't ever put feed containers out for all the hives. Second, feed your hives, if necessary only, using a method that won't attract bees from other hives (can of syrup over the inner cover or a sugar patty on the top bars). Third, make all your hives defensible by reducing the entrances. Fourth, take notice of your hives and when robbing is observed take steps to stop it (i.e. reduce the entrance further, use a robbing screen, or in dire situations remove the hive to a secluded location and take steps to increase their strength, such as giving them resources including brood from a strong hive). Also, if the hive is too weak, take off unused hive bodies to further reduce the area they need to take care of.
Signs of robbing include bees that are darting back and forth in front of the hive or bees that are flying erratically around the hive looking for a crack or hole in the hive to enter through. Unsightly buildup of wax particles on the entrance, or areas that are dirty with wax and honey at a secondary entrance (either in hive design or because the hive equipment is not tight) indicate that battles have taken place between hive occupants and robbers. If you open the hive and notice a lot of wax buildup (loose) on the bottom board this can also be a sign the hive is being robbed out.
It is my hope that by showing robber behavior in this video it will help you to become more aware of the behavior characteristics that robbing bees exhibit, and the pattern of destruction that inciting your hives to rob (by placing out feed) can lead to. I hope the video is informative!