Hornets are typically at least 4 times the size of a honeybee and have a tough exoskeleton, which can’t be penetrated by the bee’s sting, so when it comes to a straight fight, there is only going to be one winner. Hornets will often hover outside a beehive and pick off the flying bees one at a time in mid-air as they try to return to the hive. They take them back to their nest, where they remove the head and feed them to their young. But sometimes the hornets will enter the hive itself and can totally decimate the beehive, killing up to 40 bees a minute.
When attacked by hornets, European bees cluster round the entrance to the hive and form a defensive line with the bees at the front waving their legs about. From a distance it looks like a large single creature, and it’s surprisingly effective and often deters the hornets from trying to enter.
An alternative approach adopted by some species of bees is the Mexican wave defence, where all the bees gather at the entrance to the hive and move their wings in sync to create what looks like a series of waves. It has a slightly hypnotic effect, which seems to confuse the hornets.
However, Japanese bees have come up with a much better defence mechanism. First they let the hornet land and enter the hive. Then they mob the hornet with up to 50 bees piling on. Bees have a clever ability to detach their wings from their wing muscles, which allows them to beat their wing muscles to generate heat rather than movement. They use this to keep the hive warm and have very accurate thermometers in their antennae, which allows them to maintain the hive temperature typically to within a degree. However, in the case of a hornet attack, they use this ability in order to cook the hornet. It turns out a bee can withstand temperatures of up to 50 degrees, whereas hornets will die at 45 degrees, so the bees heat themselves up to exactly 46 degrees and roast the hornet alive. No idea how they worked this out, but it’s pretty effective. It’s also pretty clever that the bees managed to share this information between themselves.
Unfortunately, the European bees have yet to learn this thermo-balling approach, which is particularly worrying now that Asian hornets have begun appearing in Europe, as the Asian hornets are larger and more aggressive than European hornets and are much less likely to be deterred by the defensive line approach.
