Bumblebees have a ‘remarkably successful’ way of fighting off invasive Asian hornets: Study

Asian hornets, also known as yellow-legged hornets, have invaded large parts of mainland Europe and parts of east Asia. But now, a study has shown that they are possibly facing resistance from native species like bumblebees.

New research shows bumblebees have a remarkably successful method for fighting off Asian hornets. The study was published in the journal Communications Biology and led by a British university.

It comes at a time when a record level of Asian hornets have been observed in the UK and continental Europe this year, raising the risk for bees and prompting substantial control efforts. 

Scientists from the University of Exeter observed that when attacked, buff-tailed bumblebees drop to the ground and take the hornets down with them. This causes the hornet to either lose its grip or the bee raises its sting and tussles until the hornet gives up.

Researchers from the British university witnessed over 120 such attacks with bumblebees winning each time. However, this does not seem to be reflected in the numbers since the researchers also found that bumble bee colonies had reduced growth rates in areas with high numbers of Asian hornets. 

This suggests that the hornets – despite their failed attempts to attack and enter the colonies – have a negative impact on the pollinators. 

“Asian hornets prey on a wide range of insects, including honey bees, but little is known about their impact on other pollinators,” said Thomas O’Shea-Wheller, from Exeter’s Environment and Sustainability Institute, in a statement. 

During the so-called fight between honey bees or bumble bees it was observed that the hornets do something called “hawking” which is essentially hovering outside the colony and attacking returning foragers as they fly past, O’Shea-Wheller explained. 

Researchers also found that while hornets deploy the same method for both pollinators, with bumblebees, they are “entirely unsuccessful.” The study also noted that while honey bees are often unable to escape the clutches of Asian hornets, bumblebees’ defensive response appears to be more successful. 

Speaking about the hornets’ low success rate, the researcher also said that hornets attack bumblebees of “all sizes” even some larger than them. He added, “They are very persistent and generalist predators, so these attacks may still be worthwhile despite the high failure rate, as long as they sometimes get a kill.”

For this study, researchers placed reared bumblebee colonies in 12 locations across the Spanish province of Pontevedra with varying local Asian hornet densities. These colonies were then weighed – as a way to measure colony growth – every two days. 

Researchers noted that colonies in areas which had higher Asian hornet densities grew more slowly. “We can’t say for certain why this is. It’s possible that some external factor is good for Asian hornets, allowing them to thrive, but bad for bumblebees,” said O’Shea-Wheller.

 

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