A Fungus-farming Bee

A couple of years ago, I wrote about fungus-farming ants. These ants are a famous example of non-human animals farming, but they're hardly alone; for example, some termites, ambrosia beetles, damselfish, and snails have also been known to farm. Late last year, a research team in Brazil added a social bee to the ranks of farming animals.

The team was researching the stingless bee Scaptotrigona depilis when they noticed a white fungus growing on the inside of the wax cells where larva are reared. Their curiosity piqued, they checked 30 colonies and found the fungus in all of them. The fungus starts growing around the same time as the egg hatches. During the first three days of the larva's life, the fungus grows inwards over the larval food; after the third day, the amount of fungus drops, disappearing two days later.

Using time-lapse images, the researchers saw that the larva cut the fungus with its mandibles as it grew. When the researchers tried growing larva in cells without the fungus, only 8% of them survived, and the larval food in those cells "smelled bad and showed other signs of spoilage such as stickiness". The researchers speculated that the fungus may help preserve the larva's food, but a test against the bacteria Escherichia coli and Staphylococcus aureus didn't support their hypothesis, though it didn't disprove it, either. While the fungus wasn't effective against these bacteria, it might have an effect on other pathogens which are specific to S. depilis.

The researchers found the fungus in the building material used by the bees, a mixture of wax and plant resins called cerumen. Although the fungus was in cerumen samples from throughout the nest, it only grows when the cerumen is used to build brood cells, perhaps because it needs contact with the larval food to grow. The fact that the fungus is in the cerumen means that the workers take it with them when they go to build a new colony, which is unusual. In fungus-farming ants and some termites, the reproductive adults take fungal spores with them when they set off to found a new colony.

According to the paper, this is the first known fungus-growing bee, despite the fact that bees have been extensively studied and other social insects have been known to grow fungi. Perhaps fungus-growing is rare among bees, or maybe we just haven't thought to look for it. To me, this a wonderful reminder of how much we still have to learn — all the wonderful mysteries just out of sight in the mundane, tucked under something we've forgotten to see, made invisible by familiarity. I think we can all afford to slow down and learn to look without expectation; it's a habit I aspire to, and one I hope to inspire in tohers.

Ref
Menezes, et al. A Brazilian Social Bee Must Cultivate Fungus to Survive. Current Biology 25:2851-2855. (2015) doi:10.1016/j.cub.2015.09.028

Image credits
The image is adapted from Figure 1 in the paper.