Hornets cooked to death

Afew days ago, my Twitter feed was buzzing after a National Geographic article about the sighting of a couple of Asian giant hornets in the US. I’ve never liked hornets after being chased by a bunch of them as a kid. I remember being struck by how aggressive they were. It’s likely they were Vespula germanica, also known as German yellowjackets. Vespa

mandarinia are in a whole other league. They’re called giant hornets as they can get to 4-5 centimetres in length. And they have an impressive stinger that can deliver a very nasty venom. These hornets are found in China, India, Japan, Korea and Nepal.

In 2007, Youichi Yanagawa and colleagues from the well-named Department of Traumatology and Critical Care Medicine at Japan’s National Defense Medical College published a case study and literature review describing how the giant hornet’s venom kills 30 to 50 people in Japan each year.

But it wasn’t the wellbeing of Americans that got scientists concerned about Vespa mandarinia’s possible arrival in the US. It’s the welfare of the country’s honeybees.

Asian giant hornets are notorious for being able to destroy a honeybee colony in just a few hours.

The hornets start by entering a nest and biting off the worker bee’s heads with their large mandibles. Once all the workers are dead, they then hang out in the nest for a week or so, feeding on the pupae and larvae.

However, Japanese honeybees have developed an ingenious defence mechanism to deal with these dangerous predators. Because a honeybee’s own stinger is too small to pierce the thick exoskeleton of an Asian giant hornet, a group of worker bees will swarm around the invader forming what can best be described as a ‘‘bee ball’’.

They need to do this quickly. If they don’t, the hornet will release chemicals that attract more hornets to the nest. The bees in the ball then start to vibrate their wing muscles. This raises the temperature inside the ball to over 45 degrees Celsius.

Hornets begin to die above 44C but the bees can withstand temperatures up to 50C. The bees stay like this for more than half an hour, effectively cooking the hornet to death.

The worry is that American honeybees haven’t got the bee ball defence, so finding any Asian giant hornets that have made it to the US and stopping them from establishing will be crucial.

The hornets start by entering a nest and biting off the worker bee’s heads with their large mandibles.