The “hot bee ball” refers to a collective defense strategy in certain honeybee species. It is a coordinated behavior where hundreds of worker bees respond to a direct threat against their colony. The bees work together to create a living sphere around an invader and employ a unique method to neutralize it.
The Threat Triggering the Defense
This defense is triggered by an attack from the Asian giant hornet, a predator many times larger than an individual honeybee. A single hornet scout poses a danger, as its primary goal is to mark the hive with pheromones. This chemical signal guides the scout’s nestmates to the hive for a mass attack that can destroy the entire colony.
Once a hive is marked, a group of 20 to 30 hornets can kill a colony of 30,000 bees in a matter of hours. They are seeking the bee larvae and pupae to feed their own young. Failing to stop the initial scout guarantees the slaughter of their colony, and this predatory pressure has driven the evolution of this defensive response.
The Mechanics of the Bee Ball
When a scout hornet is detected, hundreds of Japanese honeybees swarm the invader, completely engulfing it to form a dense ball. The bees inside vibrate their flight muscles in unison, and this collective vibration rapidly generates heat. This raises the temperature at the core of the bee ball to approximately 46-47°C (115-117°F), a temperature just above the lethal limit for the hornet.
The bees maintain a precise temperature, as their own maximum thermal tolerance is only a few degrees higher at 50-52°C (123-125°F). A secondary killing factor comes into play as the bees’ metabolic activity and restricted airflow cause a significant increase in carbon dioxide levels. This combination of heat and asphyxiating conditions is fatal to the trapped hornet in under an hour.
A Co-evolutionary Advantage
This thermal defense is a specialized trait of the Japanese honeybee (Apis cerana japonica), which has shared its native habitat with the Asian giant hornet for millions of years. Their relationship is a co-evolutionary arms race, where the prey has developed a specific countermeasure to its primary predator. The bees have evolved the physiological and behavioral adaptations needed to execute this defense.
In contrast, European honeybees (Apis mellifera), which were introduced to Japan, lack this defensive behavior. Having not evolved alongside the giant hornet, their colonies are vulnerable and often destroyed by hornet attacks. The presence of the hot bee ball in one species and its absence in another highlights how predator-prey interactions can drive the evolution of survival mechanisms.