Robber screens

In 2018 the Siouxland Bee Improvement Project had some trouble with mating NUCs getting robbed out by larger nearby hives.  Robbing is what we call it when a hive gets attacked by other hives, gets overwhelmed by the sheer number of invading bees, and loses most or all of it’s honey stores to the invading honey bees.  Usually it is fatal to the colony that got robbed. I have experienced trouble with robbing on and off over the years. The first few times it happened I was surprised by how fast it kills a hive and how fast it can spread.  There is no way to predict when a year will turn out to be a bad year for robbing. And you cannot always count on it only affecting small hives. Sometimes fair to medium sized hives have trouble from robbers too. It has a tendency to happen to weak hives during a dearth in the nectar flow.  Here in Iowa we usually have a dearth the whole month of August. Most beehives have a large workforce at this time of the year but the nectar stops coming in and suddenly there is nothing for this large workforce to do. What happens is the bees continue to scout, looking for food sources and they will stumble upon a weaker colony of honeybees. The weaker colony will do it’s best to defend it’s entrance, but if there are too many bees for them to fend off then the invaders will steal the honey from the week colony and take it back to their own hive.  Usually a colony that is getting robbed is getting robbed by multiple colonies at the same time. They are getting ganged up on and have less chance of defending their entrance and protecting their honey stores.

Mating NUCs are especially susceptible to robbing due to their small size.  Keeping them in a location that is not near larger hives can help protect them from robbing.  But after you have experienced a robbing event and seen how hard it is to stop once it has started, you begin to realize it is very important to prevent this from ever getting started.  The best way I have found to prevent robbing is by using robber screens on ALL of your hives. Not just the small ones but all of them. I try to have mine all on by the 1st of August.

You can buy robber screens from most of the bee supply companies.  But they are fairly simple to make as well. In an emergency, if you suspect a hive is getting robbed and you don’t have any robber screens, you can use a piece of window screen or ¼ inch hardware cloth in front of the entrance.  Just make sure the bees living in the hive can go up and out by going around the screen.

The way the robber screen works is the invading bees find the entrance by smell while the bees that live in the hive know the location of the entrance without smell (or even sight for that matter).  So the bees that live in the hive will learn right away that they need to go around the screen to get in and out of the entrance. All that the invading bees know is that they can smell the entrance to the hive through the screen at the bottom of the hive, but they can’t figure out how to get to the entrance since the screen blocks their direct path.  Most robber screens have a solid piece the prevents the robbers from watching the resident bees walking up and down the hive front to get in and out of the entrance. This helps prevent the robbers from learning how to go around the screen.

The robber screens I make don’t have any doors that can be opened or closed.  They are single mode, always on, robber screens. Because of that, I have to put these on after dusk, when all of the bees are in their hives.  Otherwise, if I put them on too early the returning workers would be confused by them and can’t find their way back into the hive. If you put them on at night, the next time a bee leaves the hive the next morning it will have to find its way out around the screen.  And when it comes back it will remember that it had to go around the screen to get out and it will be able to reverse that to find its way back into the hive.

I build mine with 1by2 lumber, some ¼ inch hardware cloth and a lath or two.  The hardware cloth is stapled to the iby2 and the lath is nailed between 1by2’s to give the whole thing a little stability.  I drill two holes in the 1by2’s and use screws to attach to the front of the hive.

I think it is important to put these on all of your hives BEFORE robbing gets started. It is easier to prevent robbing than it is to stop it once it has started.