Why honey bees collect propolis
Although we say honey bees collect propolis, what they actually collect are the materials to make propolis. The substances the bees bring home are sap-like resins exuded from flower and leaf buds. For the plants, these resins form a defensive coating, protecting delicate plant parts from pathogens, fungi, and insects. Foraging honey bees scrape it off plants and carry it in the pollen sacks on their hind legs. It often looks like a load of pollen except that it glistens in the sunlight and is usually a rich chestnut brown. Once home, the bees mix the resins with saliva and beeswax. The final product is what we know as propolis.
The color however varies with the source. It may be a whitish gray, tan, a variety of browns, or nearly black. Its composition also varies considerably, and so do its antibacterial and antifungal properties. As a general rule it averages about 50% balsams, 30% waxes, 10% essential oils, and 5% pollen. The rest is a vast composite of amino acids, vitamins, and minerals.
Propolis has many purposes
Bees use propolis for a number of purposes. They tend to seal small cracks with it, they use it as a polish on the inside of brood cells, and they wrap dead things with it to prevent putrefaction in the hive. Dead mice and snakes—which are too big for the bees to remove—have been found completely sealed in propolis, much like a mummy. They also smear it over rough places in the hive to reduce wear and tear on their delicate wings, and sometimes will use it to reduce the size of their entrance.
As any beekeeper knows, they also use it to seal the frames to the brood box, the boxes to each other, the boxes to the bottom board, the roof to the inner cover, the inner cover to the supers, and on and on. Hence the invention of the “hive tool”—a creatively-named implement that allows the beekeeper to pry, cuss, and moan until the hive comes apart.
From sticky to brittle
When warm, propolis is gooey, stings into ropes like hot mozzarella, and is incredible sticky. When cold, it is brittle and will snap like glass. Regardless of the temperature, the bees move it to irritating (for humans) places. It is for this reason that some breeders have selected against propolis collection and have produced a few genetic lines that collect considerably less than others. As often occurs after human interference, there is now some question about whether these bees can adequately defend their hives against pathogens.
Honey Bee Suite