For use on beehive entrances
Robbing by bees or wasps is a common problem at the end of Summer. Like many problems in beekeeping it is best resolved at source by maintaining strong colonies, ensuring there are no chinks or gaps between boxes, reducing entrances when appropriate and taking proper care during feeding or the honey harvest. Weaker hives and nucs are most vulnerable and can be demoralised and depleted of stores to the point where they will fail to overwinter.
Although many beekeepers actively trap wasps - likely of limited value - and know to reduce entrances, surprising few use the simple and effective solution of anti-robbing screens. Entrances need to be severely reduced to one or two bee-widths to assist in the fight against robbers. This might work reasonably well for a small nuc but causes major bottlenecks in a busy hive. A screen provides better protection without restricting the flying bees too much.
Before describing the screens, an understanding of the underlying principles will make the application clear. Many simple solutions can then be cobbled together from material at hand. Each screen has three functional components:
Robbers are attracted to where hive scents are strongest, just outside the hive entrance. A mesh screen prevents them from entering but the hive scent distracts them from looking for other ways in. The colony learns to use new entrances that are well away from the main entrance to the hive.
This is no more than a strip of stiff plastic or wire mesh and a few drawing-pins. The mesh needs to be self-supporting with holes small enough to thwart the passage of robbers. Wire mesh is good because it will hold a shape but cheap plastic greenhouse shade mesh will do. Having reduced the entrance if needed, use the drawing pins to fasten a strip of mesh the width of the hive along the alighting board below the entrance and the brood box above the entrance. The mesh needs to be fastened across the whole width of the hive and is bent outwards to form a half-tube open at each end. Do this before the bees emerge and they will soon learn to walk the length of the tube to exit and return.
A metre of mesh will make plenty of screens at low cost. You should already have coloured drawing pins in your bee kit and a rolled strip of mesh takes up minimal space for use in emergencies. It works just as well as the more sophisticated solutions that follow and is my preferred solution.
A commercial variant made in metal sheet is available from Thorne:
Full Width Screen
Not much more complex, and more pleasing for those who prefer "proper kit", is a simple wood-framed screen. These are much used in the USA and hardly at all in the UK. A quick internet search for "robbing screens" will turn up a variety of designs and images. See Here and Here.
The basic design is a pair of wooden battens 8mm to 12mm deep and cut to ⅓ to ½ the height of a brood box. None of the dimensions are particularly critical. A sheet of mesh cut to the width of the hive and the height of the battens is then stapled to the battens. Two further thinner battens the width of the hive are fastened top and bottom of the uprights to make a rectangular frame open at the top and bottom. Staple the edges of the mesh to the cross-battens.
Designs vary at this point. I like to use two wooden pieces that will slide into the slot for the entrance block and are fastened, with an entrance gap between them, to the bottom batten. The whole unit then just slides into place instead of the entrance block. There are several other variants. With this screen, the robbers are attracted to the hive entrance as before but the bees from the colony enter and exit from above at the top of the screen.
A Fancy Solution
A colleague took the "simple solution" and developed it into a commercial product named "Wasp Out", available from Thorne Here. This replaces the entrance block and works as well against robbing by bees as it does with wasps. It can easily be constructed from square section pipe but a cut-out covered by mesh is likely better than the perforations used in the commercial version.