Guardians of the Hives: The Ingenious Defense Strategies of Asian Honeybees Against Hornets
When it comes to defending their offspring and stores, bees display remarkable teamwork. Among them, Apis cerana, the Asian honeybee, stands out for its peculiar yet highly effective defense tactics. PETBOOK editor and biologist Saskia Schneider had the privilege of witnessing these strategies firsthand.
Bees encounter numerous adversaries, but in recent times, the Asian hornet (Vespa velutina) has garnered attention as a formidable foe to our native honeybees (Apis mellifera). While they pose a significant threat here, in their native habitats, accessing bee prey, particularly to feed their offspring, proves challenging. This is due to the multiple effective defense mechanisms developed by Apis cerana against hornets, some of which are reminiscent of medieval torture methods. From deterring invaders with feces to roasting them alive, these bees have evolved ingenious strategies to counter their predators.
During a trip to Nepal, I had the opportunity to observe Asian honeybees warding off hornets. Colonies of these bees are ubiquitous among rural households, albeit yielding less honey than their European counterparts. However, they excel in repelling threats like the Asian hornet. Over millennia, Apis cerana has honed effective defense strategies, three of which stand out for their peculiarity.
Asian honeybees perform a "Mexican wave" when detecting hornets Asian hornets primarily target honeybees near hive entrances, where they lie in wait for returning foragers. While Asian bee colonies may not immediately reveal the presence of hornets, their behavior betrays their awareness. Upon detecting a hornet, bees stationed at the hive entrance begin shaking in unison, rhythmically raising and lowering their wings in a wave-like motion akin to a stadium's Mexican wave.
This visual pattern serves to confuse and warn the assailant. Observations suggest that this behavior is exclusive to encounters with hornets, with no reaction to other large insects like butterflies.
Researchers speculate that this synchronized display is not merely a tactic to disorient but a genuine warning: "We see you!" Indeed, the bees pose a threat to hornets that dare to approach, a fact not lost on the predators, as evidenced by the observed reduction in hornet attacks.
Asian honeybees repel hornets with fecal matter One of the most curious defense techniques of the Asian honeybee was discovered only a few years ago. In Vietnam, researchers observed bees collecting fecal matter from animals to line their hive entrances, particularly after attacks by Vespa soror hornets.
These hornets often assault colonies in groups, landing on hive entrances and gnawing at them. If the bees resist, a massacre ensues, with hornets making off with corpses and brood, potentially decimating entire colonies.
Remarkably, the feces at the hive entrance appear to deter hornets successfully, as observed by researchers. After all, who would willingly land in excrement? This behavior is exceptional for another reason: it marks the first instance of bees collecting non-plant material. Researchers even liken this behavior to tool usage, an extraordinary feat for insects.
Japanese honeybees roast hornets in a heat ball The Japanese subspecies of the Asian honeybee, Apis cerana japonica, has developed a highly effective tactic. When attacked by Asian hornets, bees swarm the intruder and encase it in a "heat ball" formed by vibrating their flight muscles to generate heat. This process raises the temperature inside the ball to around 47 degrees Celsius, effectively roasting the hornet alive.
Researchers believe that Asian honeybees evolved this seemingly brutal tactic because their venomous stingers cannot penetrate the thick exoskeleton of hornets. Thus, they resort to creating a heat ball, roasting their foe for up to an hour. But how do the bees themselves survive this ordeal?
The mechanisms enabling Asian bees to endure the heat ball without perishing remain unclear. However, Japanese scientists uncovered preliminary evidence in 2012. They identified a genetic code in the bees' brains that activates only at high temperatures. While the exact function of this "genetic switch" remains elusive, researchers speculate that it may signal the bees when to terminate the heat ball, preventing self-inflicted harm.
FAQ - Frequently Asked Questions:
Q: How do Asian honeybees defend against hornets? A: Asian honeybees employ various ingenious defense strategies against hornets, including synchronized shaking to deter attackers, lining hive entrances with feces to repel intruders, and forming heat balls to roast hornets alive.
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