Sometimes you’ve got to do what you’ve got to do, and for Asian honey bees (Apis cerana), this means gathering feces in their mouthparts and depositing mini-mounds of the stuff near the entrance to their nests.
"We report for the first time the remarkable employment by A. cerana of feces to defend their nests, a behavior that constitutes the first report of honey bees using a tool – a non-plant solid – to deter attack by a dangerous predator,” write the researchers in PLOS One.
To make this beautifully dirty discovery, the researchers monitored the bees over 10 days in Vietnam. Field observations revealed that A. cerana workers collect poop in their mandibles, buzz back with it to their colonies, and apply the clumps as textured spots on the fronts of their hives (called “fecal spotting”).
The team also observed them forage for feces in a nearby chicken coop, collect soap scum and, on one occasion, visit a container of human urine nearby. Another hive was dotted with mysterious bright blue spots that stumped the researchers where it came from.
A survey of 67 beekeepers who kept A. cerana colonies revealed that 63 of them (94%) noticed fecal spots on their hives. The beekeepers had between three and 170 colonies, for an average of 15 colonies each. Spots were reported on 74 percent of the hive fronts.
After learning of such dung-collecting behavior, a few questions plop forth: Why do they do this? How unique is this behavior? Are these poop spots really tool use?
Why collect feces?
Honey bees have a suite of defenses at their disposal to protect their larvae and golden goods. In particular, the honey bees in Asia have evolved under what the researchers call “tremendous predatory pressure” from giant hornets (Vespa soror), a formidable foe that attacks colonies by crushing, dismembering, and chewing prey. The giant hornets are not there for the honey though, they seek the little larvae still in their hexagonal cells, which provide a protein-rich meal for their own young.
A successful attack first starts with a scout hornet leaving a chemical trace on the “doorsteps” of the bees' home. The scout then recruits nestmates to attack and slaughter the bees, with each hornet capable of killing thousands of bees. In a few hours, the entire nest’s defenses can be wiped out. Hornets subsequently occupy the new territory, guard it as their own, and deliver the brood back to their nest to nourish their young.
There are several ways fecal spotting could help protect these honey bees from such violent attacks. “It is possible that fecal spots contain compounds that are repellent to V. soror attackers,” write the researchers, adding that “earwigs, for example, release volatiles that smell like feces to limit predation and Manduca sexta caterpillars defecate profusely on themselves as a defense against attack.”
A second possibility is that fecal spotting masks the pheromones of a hornet scout that marks the bee bounty, thereby limiting a hornet visit to just one intruder rather than an onslaught of invaders.
Another method honey bees use to defend their nests is to “roast” wasps to death with the heat of their bodies.
How unique is this behavior?
Honey bees are known to forage for materials like plants (nectar, pollen, resin) and fluids (brackish water, sweat, and vertebrate urine). To protect nest families, “defense can take the form of physical, chemical, and behavioral barriers, the combination of which are known as defense portfolios,” write the researchers.
In addition to earwigs and certain caterpillars using feces to their advantage, the “larvae of many chrysomelid beetle species repel insect and bird predators using fecal shields that they wear on their backs, in which plant defensive compounds that larvae have consumed are recycled,” write the researchers.
It’s possible the “filth foragers”, as the team call them, also sought specific compounds in the feces because they often returned to the same spots on the dung piles and pulled at the material for a while before carrying it away.
Are these poop spots really tool use?
The definition of tool use is controversial. The team believe fecal spotting meets the four key criteria set forth by Shumaker and colleagues. First, the bees employ an external environmental object (in this case feces). Secondly, they alter with “purposiveness” the object. Third, the bees directly manipulate the tool when they carry the feces from a dung pile and shape it with their mandibles around the nest. Finally, the bees orient the tool, which in this case means spotting it around the entrance where attacking hornets breach.
