Queen excluder

01 · HOW IT WORKS

4.20 mm: the worker gets through, the queen does not

The queen's abdomen is wider than a worker's, and those 4.20 mm slots are the filter. Bear in mind that drones do not get through either: if there are drones above when you put the excluder on, they will pile up against it trying to leave, so fit it when the super is clear of drones. And if brood turns up in the super with the excluder on, do not blame the gap: nearly always there is a queen or laying workers above it.

02 · SIZE AND FITTING

One orientation only, and sometimes a few millimetres to trim

It measures 421 × 506 mm, so in a 10-frame box it goes in one way only: the slots end up running across the top bars, not in line with them. On some Dadant and Italian formats it overhangs by a few millimetres on one side; being plastic, you trim it with a knife against a straight edge and it is done for good. There is no frame: it lies loose, and the weight of the super holds it down.

03 · CLEANING AND DURABILITY

Propolis comes off, and plastic does not rust

It is 2.5 mm injection moulded plastic: thicker than the thin flexible excluders, and in exchange it does not sag in the heat or dent when you scrape it. It stands up to what gets used in a hive — oxalic and formic acid — and to steam up to 119 °C, so it can be disinfected hot. Propolis comes off with alcohol, caustic soda or boiling water; unlike metal ones, there is no rust to deal with at the end of the season.

04 · BEFORE YOU BUY

This is the grid alone, with no wooden frame. It weighs 240 g and should be stored flat: stacked on edge it ends up curling.