A new study suggests that it has to do with bacteria on and in the bees’ bodies and in the food that they store in their hives. 

Researchers from the United States and the Netherlands, reporting in the journal PLoS One, say the most promiscuous queens have more “good” bacteria in their hives, and this probably improves the health and nutrition of their colonies. They did their study by inseminating queen bees with semen harvested from either 15 males or a single male. 

Colonies whose queens had more mates “had way more bacteria in them and had more probiotic bacteria, or good bacteria,” said Heather Mattila, an environmental biologist at Wellesley College and the study’s first author, “and far fewer bacteria related to plant and animal pathogens — bad bacteria.” 

Since most other social insects mate only once, honeybees probably evolved toward mating with many males, Dr. Mattila said, adding, “The bees today that mate promiscuously have a benefit over their ancestors.” 

By increasing genetic diversity through mating, honeybees seem to be able to benefit from more microbial communities. 

Several of the bacteria that were found had not been seen before in honeybee colonies. One was oenococcus, used by humans to ferment wine; another was bifidobacterium, found in yogurt.