Bumble Bees Successfully Defend Against Asian Hornets, Study Finds
New research from the University of Exeter has revealed that bumble bees have an effective method for fighting off Asian hornets. The study found that when attacked, buff-tailed bumble bees drop to the ground, causing the hornets to lose their grip or engage in a physical struggle. The researchers observed over 120 attacks and found that the bumble bees successfully defended themselves every time. However, despite their successful defensive strategy, bumble bee colonies in areas with high Asian hornet densities experienced reduced growth rates.
The research, titled “Quantifying the impact of an invasive hornet on Bombus terrestris colonies,” was published in the journal Communications Biology. Asian hornets, also known as yellow-legged hornets, have become invasive species in mainland Europe, parts of east Asia, and recently in the US. Sightings of Asian hornets in the UK and continental Europe have reached record levels this year, raising concerns for pollinators and leading to significant control efforts.
While Asian hornets are known to prey on honey bees, little is known about their impact on other pollinators. The study found that Asian hornets exhibited unsuccessful attacks on bumble bees, similar to their attacks on honey bees. The researchers placed commercially reared bumble bee colonies in different locations in Spain with varying densities of Asian hornets. The colonies in areas with higher hornet densities showed slower growth rates.
The reason for the negative impact on bumble bee colonies is still uncertain. It is possible that the presence of Asian hornets limits the success of bumble bees, or an external factor benefits the hornets while being detrimental to bumble bees. Asian hornets have been reported to consume bumble bees, and they compete with bees for food and harass them during foraging. Defending against hornet attacks can be energetically costly for bumble bees, especially when hornet abundance is high.
Thomas O’Shea-Wheller, researcher at the Environment and Sustainability Institute on Exeter’s Penryn Campus, suggested that the defensive response of dropping to the ground by bumble bees may be an “evolutionary coincidence.” Bumble bees have not evolved alongside Asian hornets like honey bees have, and their tactic appears to be more successful in evading hornet attacks.
The research team included scientists from the University of Vigo and the University of Santiago de Compostela. The study provides valuable insights into the interactions between invasive species and native pollinators, highlighting the need for further research and conservation efforts.
For more information, the study titled “Quantifying the impact of an invasive hornet on Bombus terrestris colonies” is available in the journal Communications Biology.