Queen excluder

In beekeeping, a queen excluder is a selective barrier inside the beehive that allows worker bees but not the larger queens and drones to traverse the barrier. The bars have a distance of 4.2 millimeters. The barrier grid was probably invented around 1890.

The purpose is to prevent the queen from moving from the brood chamber to the honey chamber. There she would lay her eggs between storage cells with honey, so that bee larvae or eggs would get into the honey during centrifuging.

Queen excluders are also used with some queen breeding methods.