July 5, 2009
Honeybees Form “Bee Ball” To Kill Predator
Japanese honeybees use heat and carbon dioxide to kill their natural predator, the giant hornet.
The bees form a "bee ball" in order to smother the predator, and kill the hornets within 10 minutes of their capture within the ball.
Japanese hornets feast on the honeybee's nests and can consume their larvae.
According to research, which appears in the journal Naturwissenschaften, if bees spot the attacker in time, they can stop them with their powerful "bee ball" defense.
Although, researchers found that the heat within the ball is not enough to kill the hornets on its own.
"They can survive for 10 minutes at a temperature up to 116F, and the temperature inside the bee balls does not rise higher than 114F," said Fumio Sakamoto, one of the authors of the study.
Sakamoto and his team recreated the bee balls and took measurements from inside them.
The researchers attached anesthetized giant hornets to the tip of a thermometer probe or gas detector, and then touched the probes to the bees' nest.
"The bee ball formed (around the hornet) immediately," said Dr. Sakamoto.
Within 10 minutes the bees had formed a ball around the probe.
The temperature inside the ball increased to more than 113F, and the carbon dioxide level also rose quickly.
Scientists found that as the carbon dioxide levels rose, the amount of time the hornet could survive within the ball decreased.
"So we concluded that carbon dioxide produced inside the bee ball by the honeybees is a major factor, together with temperature, involved in the bees' defense," Dr. Sakamoto told BBC News.
The researchers are still unsure if the bees were "gassing" the hornets, or just depriving them of oxygen.
"Either way, the carbon dioxide increase and/or the oxygen decrease lowered the temperature that was lethal to the hornets," he said.
"We are going to do the additional experiments about this point using mixed air of various oxygen and carbon dioxide (concentrations)."
The bees also appeared to work in "two phases".
"The hornet may be killed during the first 0-5 minute period, in which the highest level of heat production and carbon dioxide emissions take place," said Dr Sakamoto.
This suggests that the bees understand the physiological state of the hornet.
"The latter 5-10 min period may be free running to ensure their
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