Separator Grids in Rearing

A queen excluder (excluder, queen separator) is a wire or plastic sheet with gaps that worker bees can pass through but the larger-bodied queen and the drones cannot. In queen rearing it is used to protect queen cells from the queen, to keep the breeder queen on a single comb, to run a starter and a finisher in the same hive, and to control drone movement at mating sites. This page describes the excluder from a queen rearing point of view: where it is used, how to choose one, and which mistakes wipe out a batch.

How does a queen excluder work?

The gaps in an excluder are wide enough for a worker bee's thorax to pass through, but not the queen or a drone. On excluders used for bees of European origin this gap is usually around 4.1–4.4 mm. Evenness of the gaps matters more than their width: a single bent wire or cracked plastic bar creates an opening large enough for the queen to get through.

In general beekeeping the excluder is used to keep the queen in the brood box and leave the honey super free of brood. In queen rearing its job is more critical: the queen must not enter the area where the queen cells are even once. A queen that reaches the cells will tear them open from the side and kill the pupae inside.

Where is an excluder used in queen rearing?

How is an excluder used in a queenright finisher?

In a queenright finisher the queen stays in the bottom box with young brood and empty combs. An excluder is placed between the boxes; frames of open brood, pollen and honey are moved from below to the upper box, and the grafting frame is placed between them. Nurse bees pass through the excluder to tend the brood and the queen cells in the upper box.

1. Confirm where the queen is: Before putting on the excluder, see the queen and make sure you have put her in the bottom box. If she was not seen, the frames in the upper box are shaken, or you look for eggs in the upper box a few days later.
2. Check the excluder: Its frame must have no gaps, bent wires or broken bars, and it must sit on the box without gaps at the edges.
3. Look for eggs in the upper box: If fresh eggs are seen in the upper box before the cells are given or at any batch, the queen has got above; the batch is at risk.
4. Break down wild queen cells: The bees may draw their own queen cells on the brood frames moved to the upper box; check and break them down a few days after the grafted cells are given.

Types of excluder: wire or plastic?

• Framed wire excluder: Parallel wires are fixed to a wooden or metal frame and cross bars. It is sturdy, its gaps are not easily distorted, and it can be cleaned with a flame or hot water. It is the most reliable type for queen rearing.
• Plastic excluder: Light, cheap, and can be cut to fit the box. It flexes, can bend in the heat, and scratches and breaks easily when scraped with a hive tool; it needs regular checks.
• Perforated metal sheet: Made from thin punched sheet metal; the edges can be sharp and it can rust over time.

When choosing, look for gaps that are even and uniform, a sheet that sits on the hive without gaps at the edges, and resistance to bending. For bees to move comfortably between boxes, there must be a proper bee space between the excluder and the top bars of the frames.

Can a virgin queen get through a queen excluder?

Yes, she can. A laying queen has a large abdomen and is stopped by the excluder; but a newly emerged virgin queen is slim and small and can sometimes pass through the gaps. This is an important detail in queen rearing:

• A virgin queen emerging from a wild queen cell in the upper box of the finisher can go down through the excluder and fight the colony's queen, or destroy the queen cells in the upper box.
• For this reason ripe queen cells are not left until emergence day; they are distributed on day 10 or put into protective cages.
• Do not think of the excluder as a reliable barrier for holding a virgin queen; use a cage for a virgin queen.

Excluder entrances at mating sites

The security of isolated mating sites depends on only selected drones being brought onto the site. So that the boxes to be mated contain no unwanted drones, the drones are removed before the boxes are brought in, or an excluder is fitted to the entrance to stop drones leaving. Boxes holding instrumentally inseminated queens are also given an excluder at the entrance; this way the queen cannot go on a mating flight, while the workers can work freely.

Because drones cannot get out through an excluder entrance, they may pile up and die at the entrance; these boxes should be checked often and the entrance cleared.

Maintaining a queen excluder

• Scraping: Wax and propolis deposits narrow the gaps and slow traffic; scrape along the direction of the gaps with a hive tool.
• Checking: Before each use, hold it up to the light and look for bent wires, broken bars and gaps in the frame. A doubtful excluder is not used for queen rearing.
• Cleaning: Wire excluders can be cleaned with hot water or a light flame; plastic excluders are washed in hot water and never held over a flame.
• Storage: Store lying flat, with no weight on top; a bent excluder loses its correct spacing.
• Hygiene: An excluder used in a colony where disease was seen is not put on another hive without cleaning.

Common mistakes

• Not confirming where the queen is: If the queen stays in the upper box, the whole batch is lost.
• Using a damaged excluder: A single open gap makes the excluder useless.
• Trapping drones above: Drones left above the excluder cannot get out and die; leave a separate exit for the upper box.
• Relying on the excluder against virgin queens: A virgin queen can get through; distribute ripe queen cells on time.