Smelly “barricades” at the entrance: Asian honeybees use collected animal droppings to protect their hives from invasions by giant hornets, researchers report. They interpret this behavior as the first evidence of tool use in bees. The discovery could also have a meaning in connection with invasive species, the researchers say: The European honeybees, unlike their Asian cousins, could be helpless at the mercy of the giant hornets when they are introduced into their range, the researchers say.
Memories of the cartoon series “Maya the Bee” are awakened: hornets are known to be among the most important enemies of honey bees. The honey bee Apis cerana, which is widespread in Asia, is particularly affected. The giant hornet Vespa soror, which lives there, is targeting them. These downright rabid hornets are also notorious among the local beekeepers, because they can destroy entire bee colonies through mass invasions. To this end, scouts of the predatory insects, which are also state-building, mark target peoples with scents. A real invasion squadron then attacks, overpowers the guards at the entrance to the beehive and finally captures the entire brood of the colony.
But the honey collectors are not entirely helpless – researchers have already uncovered an astonishing defense concept: Since the bees can do little with their stings, they mainly take the scout hornets into a headlock. To do this, they form a cluster around the insect and thus generate lethal temperatures. But as the researchers at Heather Mattila Wellesley College in Massachusetts are now reporting, this is not the only amazing defense strategy used by Asiatic honeybees.
On the trail of “disreputable” behavior
The impetus for the study was provided by an observation by the researchers as part of investigations with beekeepers in Vietnam: They noticed strange stains at the entrances to the beehives. According to the locals, it was animal dung and they have already associated this material with an effect on hornet attacks. So the researchers decided to get to the bottom of the phenomenon scientifically.
To do this, they first collected the dung from water buffalos, chickens, pigs and cows and placed it in piles near experimental beehives. The team tagged individual bees so that they could be identified and recorded videos of what was going on in the manure heaps and at the hive entrances. It turned out that the bees preferred to collect the particularly strong-smelling dung from pigs and chickens. They then transported the chunks to the hive and carefully placed them on the surfaces in the entrance area.
The researchers then set their sights on the behavior of the hornets. It became apparent: “The more intensely the entrance of a beehive was covered with stains of faeces, the less often the predatory insects were there,” says Mattila. The scientists report that sticks armed in this way were much less exposed to one of the devastating mass attacks by the hornets. They were also able to show that the bees provided more and more excrement barricades when the predatory insects increased their visits. However, this behavior was not triggered by contact with a significantly less dangerous species of wasp.
Apparently, the reaction has something to do with a volatile substance, emerged from further experiments: The scientists extracted the pheromone that the scout hornets use to mark a target stick. When they applied this substance in the entrance area of the beehive, it caused the bees to apply more dung, the observations showed. So far, the researchers have not been able to say exactly what causes the repelling effect. It could be that the smell of the feces scares the hornets off. However, it may also cover the marking substances and thus reduce the likelihood of a mass attack.
A special kind of tool use
The scientists now interpret the behavior as the first evidence of tool use in honey bees. “Scientists disagree on the extent to which one can speak of tool use in insects,” says co-author Gard Otis of the University of Guelph in Ontario. But he and his colleagues believe that the current case fulfills the criteria: “In order to qualify as tool users, animals have to meet several criteria, including the use of an object from the environment – in this case crap. The bees clearly use the material to specifically modify the beehive, in addition to meeting the requirement to hold or manipulate the tool, ”says the researcher. His colleague Mattila adds: “Just collecting dung is something new,” she emphasizes. Honey bees routinely look for materials produced by plants – such as nectar, pollen, and resin – but they were not previously known to collect solid materials from other sources, the scientist explains.
As the researchers finally emphasize, the discovery could also have a more far-reaching significance: There is a risk that particularly aggressive Asian hornet species will spread in the areas of distribution of the European honey bee (Apis mellifera). Since these bees do not have the defensive behavior that has now been discovered, they could be particularly helpless against the invaders, according to the scientists.
Source: University of Guelph, Wellesley College, Articles: PLOS ONE, doi: 10.1371 / journal.pone.0242668