Japanese researchers have found that honeybees "gas" giant hornets that they trap inside "bee balls".
Scientists previously believed that the bees defended their nests from the giant predators by "cooking" them to death.
But a study published in the journal Naturwissenschaften, has now shown that the high level of carbon dioxide, as well as the heat produced inside the ball, kills the hornets.
During the experiment, the scientist fixed giant hornets to the ends of probes that measured temperature and the concentration of carbon dioxide.
When they placed the probes near the honeybees' nest, the bees mobbed and smothered the hornets, allowing the scientists to take measurements from inside the bee ball.