Scientists at the University of Exeter have made a remarkable discovery regarding the defensive tactics of buff-tailed bumblebees when facing attacks from invasive Asian hornets. These findings, published in the journal Communications Biology, shed light on the bumblebees’ unique ability to combat this threat.
When confronted by Asian hornets, buff-tailed bumblebees employ a surprising defense mechanism – they drop to the ground. This tactic has proven highly effective, often causing the hornets to lose their grip or engaging in a physical struggle until the hornet retreats. Astonishingly, researchers from the University of Exeter observed over 120 such encounters and found that the bumblebees successfully repelled the hornets every time.
However, despite this impressive defense, bumblebee colonies in regions with a high density of Asian hornets experience reduced growth rates. This suggests that while the hornets’ attacks at colony entrances are often unsuccessful, they still have a detrimental impact on bumblebee populations. Asian hornets, also known as yellow-legged hornets, have rapidly spread across mainland Europe and parts of Asia and have recently been spotted in the United States. The increasing sightings in the UK and continental Europe have raised concerns for pollinators and prompted extensive control efforts.
The predatory behavior of Asian hornets has been observed to include “hawking,” where they hover outside bees’ nests and attack returning foragers. Remarkably, the hornets employ a similar strategy against bumblebees, although with limited success, as documented in this study.
To investigate the impact of Asian hornets on bumblebee colonies, commercially reared bumblebee colonies were placed at various locations in the province of Pontevedra, Spain, with varying hornet densities. The study measured colony growth by weighing them every two days, revealing that colonies in areas with higher Asian hornet densities grew more slowly. While the exact cause of this phenomenon remains uncertain, it is suggested that the presence of Asian hornets may limit the success of bumblebee colonies.
Moreover, while the observed attacks at colony entrances were mostly unsuccessful, bumblebees are known to be part of Asian hornets’ diet. Defending against such attacks is energetically costly, especially when hornet abundance is high, potentially affecting bees’ foraging efforts and food competition.
Intriguingly, buff-tailed bumblebees have not coevolved with Asian hornets, making their successful defensive response of dropping to the ground a potential evolutionary coincidence. This adaptation appears to be more effective than the response of honey bees, which often struggle to escape the grasp of Asian hornets during aerial attacks.
This research, funded by the Biotechnology and Biological Sciences Research Council (BBSRC) and the European Regional Development Fund (ERDF), was conducted in collaboration with scientists from the University of Vigo and the University of Santiago de Compostela. The study’s findings provide valuable insights into the ongoing struggle between pollinators and invasive species, highlighting the complex interactions within ecosystems.
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Frequently Asked Questions (FAQs) about Bumblebee Defense
What is the key finding of the research on bumblebee defense against Asian hornets?
The research reveals that when attacked by Asian hornets, buff-tailed bumblebees employ a unique defense mechanism by dropping to the ground, effectively repelling the hornets.
What is the impact of Asian hornets on bumblebee colonies?
While bumblebees display an effective defense strategy, colonies in areas with a high density of Asian hornets experience reduced growth rates, indicating that the hornets still have a negative impact on bumblebee populations.
Why is the presence of Asian hornets concerning?
Asian hornets have rapidly spread across Europe and parts of Asia and have recently been reported in the United States. Their increasing presence raises concerns for pollinators and has prompted extensive control efforts.
How was the study conducted?
The study involved placing commercially reared bumblebee colonies at different locations with varying Asian hornet densities in Pontevedra, Spain. Colony growth was measured by weighing them every two days.
Why do buff-tailed bumblebees drop to the ground when attacked?
Buff-tailed bumblebees have not coevolved with Asian hornets, making their defensive response of dropping to the ground possibly an evolutionary coincidence. This adaptation appears more successful than the response of honey bees.
What funding supported this research?
The research was funded by the Biotechnology and Biological Sciences Research Council (BBSRC) and the European Regional Development Fund (ERDF).
More about Bumblebee Defense
- University of Exeter’s Research Announcement
- Communications Biology Journal Article
- Biotechnology and Biological Sciences Research Council (BBSRC)
- European Regional Development Fund (ERDF)
