Call it death by a thousand breaths. When hundreds of honeybees envelop a giant, enemy hornet in a ball, the bees aren’t just putting on the heat, as researchers had thought. Carbon dioxide levels spike along with temperature, fingering suffocation as the hornet’s cause of death, scientists report online and in an upcoming Naturwissenschaften.
Bees inside the ball can apparently cope with the smothering heat and low oxygen levels, but the high temperature appears to make giant hornets, Vespa mandarinia japonica, less tolerant of cranked-up carbon dioxide. The concentration of CO2 in the air increases to 3.6 percent after the bee ball forms, dropping sharply to lower levels five minutes later, report Michio Sugahara and Fumio Sakamoto, both of Kyoto Gakuen University in Japan.