Honeybee mobs smother big hornets

Honeybees of the Cyprian strain can kill an attacking hornet by ganging up and smothering it.

That tactic is new to scientists, says Alexandros Papachristoforou of Aristotle University of Thessaloniki in Greece, although it resembles an Asian honeybee species’ so-called heat-balling defense. When using that maneuver, the Asian bees cluster around a marauding hornet of another species and cook it to death with their body heat.

With Cyprian bees and the hornet Vespa orientalis, however, “we noticed some things that didn’t match,” says Papachristoforou. Cyprian bee balls warm to only 44°C. Tests show that a hornet kept at that temperature takes almost 2.5 hours to die, but Cyprian bees dispose of their foe in just 1 hour.

The researchers observed that Cyprian bees first surround the abdomen of the hornet, where its breathing holes are. Unlike most other insects, a hornet breathes by abdominal contractions.

To see whether suffocation contributed to a hornet’s demise, Papachristoforou and his colleagues smother proofed hornets by positioning tiny plastic blocks under each abdominal plate to keep the bee mob from pressing them down and covering the holes. With breathing holes propped open, hornets survived twice as long as usual in bee mobs, the researchers report in the Sept. 18 Current Biology.

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.

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