The stinking exercise of the bees

Not everything is honey in the lives of bees, especially if they live in Asia. The Asian honey bees (Apis cerana) are under constant threat from wasps, which attack their hives, kill the adult bees and eat the larvae and eggs. In Vietnam, the most dangerous enemy of bees is a giant wasp of the species Vespa soror, very close to the Asian giant wasp, V. Mandarinia, which has been nicknamed a killer wasp and has recently arrived in the United States as well. These wasps are much larger than the bees, and they hunt in groups: when one of them notices the hive, it returns to the nest and recruits its companions, sometimes several dozen of them. Each wasp can kill thousands of bees, and together they manage to destroy entire hives and take over them.

During their evolution the bees developed ways to defend themselves against the deadly wasps. They take care to keep the opening for a small hive, and place guards around it who will try to prevent the wasps from biting and expanding it and thus enter. The sting of the bees is not particularly effective against wasps, but they have developed another method of harming threatening enemies: the bees form a kind of dense ball around the wasp, thus suffocating it and heating it until it dies.

The study began when Canadian researcher Guard Otis examined hives in Vietnam and found that in many of them, the area around the development was covered with strange brown-gray spots. When he asked the beekeepers, most of them told him they did not know what this substance was, but one of them replied: “The bees do this when they are attacked by wasps. And I’m pretty sure it’s feces – I saw them pick it up from the field where the water buffalo graze.”

At first glance the idea seems rather strange, and mostly very uncharacteristic of bees. “We think of bees as insects that visit beautiful flowers and collect sweet nectar,” said Rachel Bonoan, an American bee researcher who was not involved in the study, in an interview with the New York Times. “It sounds like the complete opposite.”

Despite this, the researchers’ observations suggested that this is exactly what the bees do. Heather Mattila, who led the study with Otis, recounted the day she first saw a bee landing on a chicken droppings, taking some of it and flying back to the hive. “I remember running back to the hives, screaming ‘That’s right! Finally, that’s right!'” She said.

In the second stage, the researchers placed piles of feces collected from various animals near the hives, to examine the behavior closely. The bees flew over the stinking piles again and again, gathering some of the material, and sticking it near the opening of their hive. Matila said the bees seemed to be looking for something specific in the feces pile, perhaps a particular molecule or compound. “It’s like a flea market – they’re looking at the top of the pile, looking at it,” she said in an interview with the journal Science. “Clearly there was a purpose to their search.”

The researchers showed that the bees increased this behavior, and infected more feces, after wasps of the genus V. soror visited the hive – but not after other wasps arrived, which are not so deadly to the bees. Apparently, it was the smell of wasps that pushed the bees to fetch more and more feces: when researchers placed near the hive opening a paper that carried fluid from the wasp’s glands, and apparently contained its pheromones, the bees responded by increasing feces sticking around the opening.

The next question was, is this remedy really effective? It seems so: hives that had many fecal spots were attacked less than hives in which the bees did not put enough of the stinking substance. The wasps still visited the hives adorned with feces, but their visits were shorter, and they were less likely to land on the hive and try to widen the opening so that they could enter.

However, researchers still do not know why wasps move away from hives with many fecal spots. The material may repel them, and they are reluctant to bite the edge of the hive opening and widen it, if that means getting full mouthfuls of buffalo feces. The feces contain many compounds that come from plants, and it is possible that one or more of them have a strong effect on the wasps and they take care to stay away from them – if this is indeed the reason and if so, what substances are involved.

It is also possible that the feces serve as a kind of camouflage, in that it disguises the smells of the hive – the pungent smell of the feces may outweigh the smell of honey and wax that attracts wasps. In addition, a wasp that notices a hive that seems to be a good target for attack often marks it with a special scent, which directs it and the other wasps it has recruited when they return to destroy the hive. The smell of feces may obscure this smell as well, thus reducing the chance that the wasps will find the hive again and attack it. However, Matila said, this possibility is less likely, as wasps always mark the hive they have found in several places, and fecal points are concentrated around the opening only.

Whatever the reason, it is clear that Asian honey bees have found a way to reduce wasp attacks on their hives. In contrast, European honeybees (Apis Mellifera) did not develop this trick, as during their evolution they were not exposed to attacks by these wasps. Now that the Asian giant leper has arrived in the United States, could the new study help beekeepers, who mainly breed European honey bees, defend themselves against the deadly invasion?

Not immediately, Matila said: “The last thing we want is to spray the colonies with watery feces and hope it will help deter the killer wasps.” But if researchers can figure out exactly what substances cause wasps to move away from feces, they may be able to be used to protect bees in America. Meanwhile, Bonuan adds, it is worth remembering that even if it helps bees, feces are still not a panacea: “If you are a human, do not use poop to try and protect yourself from a killer wasp.”

Dr. Yonat Eshhar, Davidson Institute of Science Education