When temperatures drop, a honeybee colony pulls itself into a tight, living ball called the winter cluster. Bees on the outer shell (the mantle) pack shoulder to shoulder, insulating a warmer core where bees shiver their flight muscles to generate heat. The whole cluster slowly shifts across the comb as it eats its way through honey stores — and that migration is where winter colonies live or die.
Isolation starvation is one of the leading recorded causes of winter colony loss — beekeepers regularly open a dead hive in spring to find frames still heavy with honey, just one comb-width away from where the cluster finally ran out of reach and out of fuel.
A 3D cutaway hive showing a honeybee colony's winter cluster contracting against the cold, slowly migrating across honey frames as it feeds, and — depending on the conditions you set — either riding out the winter or dying with honey still in the hive.
How outside temperature, colony size and varroa load interact through a simple thermal and consumption model to determine core cluster temperature, honey burn rate, and whether the cluster can migrate onto fresh stores before local honey runs out.
Set the outside temperature, starting colony size and varroa load, then run the clock forward with the sim-speed slider. Toggle "Force isolation" to see a cluster die of isolation starvation — surrounded by full frames it can no longer reach.
Isolation starvation is one of the most common recorded causes of winter colony loss: post-mortem inspections often find frames still packed with honey just one comb-width from where the cluster finally gave out.