Research from North Carolina State University shows that honey bees "self-medicate" when their colony is infected with a harmful fungus¹, bringing in increased amounts of antifungal plant resins³（树脂） to ward⁴ off the pathogen. "The colony is willing to expend⁵ the energy and effort of its worker bees to collect these resins," says Dr. Michael Simone-Finstrom, a postdoctoral research scholar in NC State's Department of Entomology and lead author of a paper describing the research. "So, clearly this behavior has evolved because the benefit to the colony exceeds the cost."

Wild honey bees normally line their hives with propolis（蜂胶） , a mixture of plant resins and wax that has antifungal and antibacterial properties. Domesticated⁶ honey bees also use propolis, to fill in cracks in their hives. However, researchers found that, when faced with a fungal threat, bees bring in significantly more propolis -- 45 percent more, on average. The bees also physically⁷ removed infected larvae⁸（幼虫） that had been parasitized by the fungus and were being used to create fungal spores⁹.

Researchers know propolis is an effective antifungal agent because they lined some hives with a propolis extract and found that the extract significantly reduced the rate of infection.

And apparently¹⁰ bees can sometimes distinguish harmful fungi¹¹ from harmless ones, since colonies did not bring in increased amounts of propolis when infected with harmless fungal species. Instead, the colonies relied on physically removing the spores.

However, the self-medicating behavior does have limits. Honey bee colonies infected with pathogenic bacteria did not bring in significantly more propolis -- despite the fact that the propolis also has antibacterial properties. "There was a slight increase, but it was not statistically¹² significant," Simone-Finstrom says. "That is something we plan to follow up on."

There may be a lesson here for domestic beekeepers. "Historically, U.S. beekeepers preferred colonies that used less of this resin², because it is sticky and can be difficult to work with," Simone-Finstrom says. "Now we know that this is a characteristic worth promoting, because it seems to offer the bees some natural defense¹³."