Give them room first

Of the four swarm triggers, congestion is the one you can undo before it becomes a decision, and space is the cheapest intervention in this book. Room for bees, though, is not room for the queen: a later chapter tells the two apart.

Once the box is roughly seventy to eighty percent full of bees and stores, add another ahead of the need, not after the colony strains against it.

A colony that runs out of room does not wait for you to notice: it backfills nectar into the cells the queen needs for eggs, which compounds the crowding that started it.

Adding room early does not guarantee a colony will not swarm, since backfilling, nurse surplus and queen age can each push that way alone, but it removes the commonest and most preventable cause.