To raise queens on demand, beekeepers graft day-old worker larvae from a donor colony into artificial queen cups on a bar, then place the bar into a cell-builder colony — a strong, well-fed, queenless (or queen-excluded) colony primed to draw out royal jelly-fed queen cells. Around day 16 from grafting a virgin queen chews her way out. Separately, an old or failing queen is replaced (requeening) by removing her and introducing a new, already-mated queen using a method chosen to protect her from the colony's instinct to reject strange queens by "balling" her.
Because queens develop from the same fertilised eggs as workers, timing is everything: a larva grafted after roughly 24–36 hours old will still become a queen but a smaller, shorter-lived one — which is why experienced grafters prize very young, barely-visible larvae floating in a pool of royal jelly.
Graft larvae into queen cups on a cell-builder bar and step through 16 days of queen cell development, then run a requeening introduction to see whether a candy cage, push-in cage or direct release results in the colony accepting — or balling — the new queen.
A stronger, well-fed, queenless cell-builder colony draws out far more of the grafted cups; queen cells lengthen, cap over around day 8–9 and darken through pupation before a virgin emerges near day 16. Acceptance during requeening rises with a longer queenless wait and with more gradual, protected introduction methods.
Scrub the day slider to watch cell development on the bar and choose a cell-builder strength to change graft take rate. On the right, pick an introduction method and queenless duration, then press "Run introduction" to watch the candy erode or the cage lift and see the worker cluster stay calm or tighten into a defensive ball.
Master beekeepers can graft several hundred larvae an hour with a fine grafting tool, transferring each barely-visible larva without breaking the pool of royal jelly it floats in — disturbing the jelly is one of the biggest causes of a graft failing to "take".