The interaction between hornets and bees is a compelling predator-prey relationship. This predatory behavior, while natural, significantly impacts bee populations. Understanding this dynamic offers insights into the balance of nature and challenges faced by bee colonies.
Specific Hornet Species That Prey on Bees
Not all hornet species target bees, but several are known for their focused predation. The Asian giant hornet (Vespa mandarinia) is a large and formidable predator native to East and Southeast Asia, posing a significant threat to honeybee colonies.
Another notable species is the yellow-legged hornet (Vespa velutina), originating from Asia and now an invasive species across parts of Europe. This hornet frequently preys on bees at hive entrances. The European hornet (Vespa crabro), native to Europe, Russia, and parts of Asia, also preys on bees. These hornet species are characterized by their size and robust exoskeletons.
Primary Motivations for Hornet Predation
Hornets kill bees primarily to obtain protein, which is crucial for the development and growth of their larvae. Adult hornets sustain themselves on nectar, fruit sugars, and other carbohydrates for energy. However, their young require a protein-rich diet. Bees provide an abundant and accessible source of this essential nutrient.
A single honeybee colony, housing thousands of individuals, represents a substantial food resource for a hornet nest. Bees are an ideal prey due to their size and nutritional content, including protein-rich pollen and nectar-filled stomachs. This dietary requirement for their brood drives the predatory behavior in many hornet species, especially during late summer and early fall when hornet nests are at their peak.
Hornet Hunting Tactics
Hornets employ various methods to hunt bees, ranging from individual attacks to highly organized group assaults. A common tactic involves individual hornets “hawking” or hovering outside a beehive entrance, waiting to intercept foraging bees. Once a bee is caught, the hornet will often fly to a nearby perch to dismember its prey, typically removing the head, wings, and legs, and carrying the protein-rich thorax back to its nest to feed its larvae.
More organized attacks, often by species like the Asian giant hornet, involve a “slaughter phase” where multiple hornets coordinate to decimate a bee colony’s adult population. A scout hornet may chemically mark a bee nest, recruiting others to the site. These mass attacks can kill thousands of bees within a few hours, overwhelming the colony’s defenses to gain access to the bee brood and honey. The hornets then plunder the nest, carrying bee carcasses and larvae back to their own nests.
Consequences for Bee Colonies
Hornet predation can have severe consequences for bee colonies, impacting their health and survival. Sustained attacks deplete a colony’s workforce, as hornets continuously capture or kill foraging and guard bees. This reduction in the number of active bees leads to decreased foraging activity, meaning fewer resources like nectar and pollen are brought back to the hive.
The constant presence of hornets can also induce stress in bee colonies, causing bees to reduce their flight activity and become reluctant to leave the hive. This stress and reduced foraging can weaken the colony, making it vulnerable to disease and reducing its ability to build honey stores for winter. In severe cases, particularly with invasive hornet species, such pressures can lead to colony collapse or absconding, where the remaining bees abandon the hive entirely. These losses have significant implications, especially for managed honeybee populations.
Bee Colony Defenses
Bees have evolved various defensive mechanisms to counter hornet attacks, both individually and collectively. Individual bees may use alarm pheromones to alert nestmates to an approaching threat, prompting defensive reactions. Guard bees often form a barrier at the nest entrance to deter hornets from entering.
A highly specialized collective defense, particularly effective in some Asian honeybee species, is “heat balling.” When a hornet enters the hive, hundreds of worker bees will swarm and surround it, forming a tight ball. By rapidly vibrating their flight muscles, they generate heat, raising the temperature inside the ball to a level lethal for the hornet (around 46 degrees Celsius) but tolerable for the bees. This coordinated effort can effectively “cook” the invader. Some bees also use visual displays, such as synchronized “Mexican waves,” to deter hornets by signaling a united front.