How do bees defend their hives from intruders?

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Defensive Strategies of Bees to Protect Their Hives from Intruders

Guard Bees and Alarm Pheromones

Honeybees (Apis mellifera) have a highly organized system for defending their hives, primarily managed by specialized worker bees known as guard bees. These guards are responsible for identifying and responding to threats. When a threat is detected, guard bees release alarm pheromones, which recruit other bees to join the defense. These pheromones trigger both immediate and long-term behavioral changes in nearby bees, priming them for defensive actions. The neural mechanisms behind this response involve the upregulation of serotonin and dopamine levels in the brain, which increases the likelihood of an individual bee attacking and stinging the intruder.

Physical Barriers and Task Allocation

In newly divided colonies of stingless bees, such as Tetragonula iridipennis, bees employ several physical strategies to defend their nests. They build complex nest entrances and engage in nest closure behaviors to protect against intruders like resin bees, ants, and spiders. Task allocation within the colony is also crucial, with a significant portion of bees dedicated to repairing hive entrances and developing colony architecture. Similarly, Apis cerana uses animal feces to create barriers around nest entrances, deterring attacks from giant hornets (Vespa soror) by repelling them with the feces' properties.

Aggressive Defense and Nest-Site Competition

Honeybee swarms also exhibit aggressive behaviors when competing for nest sites. During house-hunting, scouts from different swarms may engage in agonistic interactions to secure high-quality nesting cavities. The level of aggression increases with the number of scouts present, leading to mobbing and even killing of scouts from competing swarms. This competitive behavior underscores the importance of securing a safe and suitable nesting site for the colony's survival.

Species-Specific Defense Mechanisms

Different species of honeybees in Thailand exhibit unique defense strategies based on their size, nest site, and predation threats. For instance, Apis florea builds nests in dense, shrubby vegetation, making them hard to find but easy to overpower once discovered. In contrast, Apis dorsata, which nests in tall forest trees, relies on massive stinging attacks from large colonies to fend off predators. Apis cerana, which nests in cavities, uses small entrance openings to prevent large predators from entering, while smaller predators are overpowered by entrance guards.

Behavioral Recognition and Response

Guard bees at the hive entrance play a crucial role in recognizing and responding to intruders. They use scent to identify members of their own colony and distinguish them from outsiders. Intruders that exhibit submissive behavior are extensively examined but not stung, while those that attempt to escape are immediately seized and stung. This behavior ensures that only genuine threats are neutralized, minimizing unnecessary aggression.

Cooperative Defense and Division of Labor

In the stingless bee Tetragonisca angustula, two distinct types of entrance guards are employed: standing guards and hovering guards. These guards work in tandem to protect the nest, with some bees specializing in one type of guarding behavior. This division of labor enhances the colony's overall defensive capabilities. Similarly, Cyprian honeybees (Apis mellifera cypria) exhibit two contrasting defensive tactics: some colonies increase the number of guards to attack and kill hornets, while others retreat and form a defensive line, using propolis walls to block hornet access.

Conclusion

Bees employ a variety of sophisticated and adaptive strategies to defend their hives from intruders. These strategies range from the release of alarm pheromones and physical barriers to aggressive defense and specialized task allocation. Each species and colony adapts its defense mechanisms based on environmental conditions and specific threats, ensuring the protection and survival of the hive.