Honeybees don't just kill hornets with heat — they gas them, too. The giant hornet (Vespa mandarinia japonica) is a ferocious predator of the Japanese honeybee (Apis cerana japonica). The bees fight back by smothering the invader inside a ball formed by their swarming bodies, killing the hornet in minutes. It was thought that the temperature inside the ball — which can rise to around 46 °C — killed the hornet while sparing the more heat-tolerant bees.
Michio Sugahara and Fumio Sakamoto of Kyoto Gakuen University, Japan, found that outside a bee ball, hornets survive such temperatures. Their heat tolerance falls, however, as carbon dioxide levels rise. The air in a bee ball contains about 3.7% CO2, and in this atmosphere the temperature is lethal to the hornet.
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Animal behaviour: Smothered by a swarm. Nature 460, 308 (2009). https://doi.org/10.1038/460308a
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DOI: https://doi.org/10.1038/460308a