Propolis is a resinous "bee glue" made when foragers scrape sticky resin from tree buds, bark wounds and leaf exudates, mix it with wax and enzymes in their mandibles, and pack it home in the same corbiculae (pollen baskets) they use for pollen. Only a small, specialised subset of foragers ever collect resin — it is a distinct, often lifelong task specialisation, not something every worker does.
Inside the hive, propolis does three jobs: it seals small gaps and cracks in the nest cavity (bees plug draughts and stop rot with it, but build wax comb across larger openings instead), it acts as a thin sterilant coating across the interior surfaces of the nest, and — for intruders too large to drag out, like a mouse carcass — it embalms the corpse in a hard resin shell so it cannot rot and seed disease inside the colony.
Humans have exploited propolis's antimicrobial reputation for millennia — it turns up in traditional wound dressings, modern cosmetics and dental varnishes, and its exact chemical fingerprint changes with whatever local trees the colony's foragers happen to be raiding.
Watch resin foragers ferry sticky bud resin from a tree back to the hive, where it seals a wall crack or slowly mummifies an intruder — while an antimicrobial coating suppresses microbial load nearby.
Only a subset of the colony forages resin at any time; the deposited propolis coating both plugs gaps and — thanks to its chemistry — suppresses microbes on contact.
Set the forager share, pick a target (wall crack or intruder), tune hive temperature and antimicrobial potency, and watch the coating and microbial-load readouts respond live.
When bees can't drag a dead intruder like a mouse out of the hive, they entomb it in propolis instead — a resin "mummy" that keeps it from rotting and spreading disease.