Propolis (yellow) lining the inside of a beehive.
Beekeepers would love to get rid of propolis, a sticky substance made of resins that bees use to line their hives, because it makes it hard to pry hives open. But propolis isn’t just gluing the hive together, according to a new study published in PLoS ONE—honeybees use it to fight off fungal infections and seek it out when their hives are infected.
Bees have to invest effort in hunting down the resins that make up propolis, which like nectar is foraged from plants. That means that every minute a bee is looking for resin is a minute it’s not looking for food. The trade-off is worth it, apparently, because propolis kills bacteria and fungi lurking in the colony.