Bees use excrement to defend themselves against giant hornets
Asian bees have developed an extraordinary technique to defend themselves against attacks by giant hornets. They cover their hive with animal droppings.
By Julie Kern, Futura Planet
The life of a bee is far from easy. In addition to its daily task of collecting nectar from flowers, a colony must also protect itself against attacks by other insects, in particular hornets of the genus Vespa. To defend themselves, bees have developed several techniques; the most impressive is undoubtedly suffocation, in which a group of bees surrounds a hornet until it dies from overheating.
Hornets also use sophisticated attack techniques: with their powerful mandibles, they chew at the entrance of hives in an attempt to penetrate them, or they leave chemical markers at the hive entrance. These markers serve as signals for a potential coordinated mass attack by several workers, which can then decimate an entire colony.
Bees that are most exposed to hornet attacks have developed a technique that had never previously been documented. Workers search for animal droppings and place them at the entrance of their nest to repel hornets. This behaviour represents the first description of the collection of non-plant material and of tool use in bees. It was observed in the Asian species Apis cerana in Vietnam and described in Plos One.
Droppings to drive away hornets
The experiments were carried out in Vietnam after several beekeepers reported the presence of droppings at the entrance of their hives. Several Apis cerana colonies were monitored for ten days. Entomologists observed the bees bringing small balls of animal droppings back to the hive, held in their mandibles, following visits by an Asian hornet species, Vespa soror.
Several days after hornet attacks, the bees continued to place droppings in front of the nest entrance. Scientists proposed several explanations for this novel behaviour. They believe that the droppings protect the nest entrance from hornet mandibles. In the presence of fecal pellets, hornets spent 94% less time chewing at the nest entrance when they landed there.
A second explanation is that the smell of the droppings masks the chemical markers left by hornets. These markers indicate the location of the hive for potential mass attacks. Bees collect droppings only when they have been attacked by aggressive species such as Vespa soror. When confronted with smaller hornets that do not carry out mass attacks, such as Vespa velutina, they do not adopt this defensive strategy.
Unfortunately, European honeybees do not use this defensive strategy and are particularly vulnerable to invasive Asian hornet species.
“The use of animal feces by Asian honeybees highlights the impressive arsenal of weapons they have evolved to defend their colonies against one of their most dangerous predators. It also helps explain why European honeybees, which lack these defenses, succumb so easily to giant hornets when the two species meet,” the authors of the study explain in a press release.
Abstract
Honeybees (genus Apis) are well known for the impressive suite of nest defenses they have evolved to protect their abundant stockpiles of food and the large colonies they sustain. In Asia, honeybees have evolved under tremendous predatory pressure from social wasps in the genus Vespa, the most formidable of which are the giant hornets that attack colonies in groups, kill adult defenders, and prey on brood. We document for the first time an extraordinary collective defense used by Apis cerana against the giant hornet Vespa soror. In response to attack by V. soror, A. cerana workers foraged for and applied spots of animal feces around their nest entrances. Fecal spotting increased after colonies were exposed either to naturally occurring attacks or to chemicals that scout hornets use to target colonies for mass attack. Spotting continued for days after attacks ceased and occurred in response to V. soror, which frequently landed at and chewed on entrances to breach nests, but not Vespa velutina, a smaller hornet that rarely landed at entrances. Moderate to heavy fecal spotting suppressed attempts by V. soror to penetrate nests by lowering the incidence of multiple-hornet attacks and substantially reducing the likelihood of them approaching and chewing on entrances. We argue that A. cerana forages for animal feces because it has properties that repel this deadly predator from nest entrances, providing the first report of tool use by honeybees and the first evidence that they forage for solids that are not derived from plants. Our study describes a remarkable weapon in the already sophisticated portfolio of defenses that honeybees have evolved in response to the predatory threats they face. It also highlights the strong selective pressure honeybees will encounter if giant hornets, recently detected in western North America, become established.
See also:
- The Asian hornet is arriving in Switzerland
- Vespa velutina, Asian hornet
- Quick reference: Vespa velutina, Asian hornet
