Analysis: The major concerns around this invasive species are to do with their impact on honeybees, beekeeping and wild insects
By Dara Stanley, UCD
After years of anticipation, the Asian hornet has finally arrived in Ireland, but it's not a welcome sight. Following the first sighting of a single individual in 2021, the first fully established nests were located in Cork earlier this month. A co-ordinated response by the National Biodiversity Data Centre, the National Parks and Wildlife Service and others has resulted in their swift eradication.
The Asian Hornet (Vespa velutina nigrithorax, also known as yellow-legged hornet) is one of over 20 species of hornet globally, most of which are found in Asia. It was accidentally introduced to Europe in 2004, and has since spread rapidly through France and neighbouring countries. The first sighting in Spain was in 2012, with thousands of colonies now reported every year. The Asian hornet is on the EU list of Invasive Alien Species of Union Concern.
We need your consent to load this rte-player contentWe use rte-player to manage extra content that can set cookies on your device and collect data about your activity. Please review their details and accept them to load the content.Manage Preferences
From RTÉ Radio 1's Oliver Callan Show, Biodiversity Officer at TCD Collie Ennis on why bees are under grave threat because of the destructive Asian hornet
While the Asian hornet is firmly established in mainland Europe, the UK are still working hard to keep it out. Over the last number of years an eradication programme has been in place, with 96 nests found this year to date. Most of these nests are considered new introductions, with almost no signs of overwintering in the UK.
Nests are significant: mature nests can produce up to 13,000 individuals over their lifespan, with up to 500 queens produced. In SW France, males emerge in early September with the first queens about two weeks later and continuing to a peak in November. It is crucial to eradicate nests before the reproductives are released, to minimise chances of a population establishing.
With the Asian hornet infiltrating the UK, and the many transport links between Ireland and mainland Europe, it was only a matter of time before Asian hornets made their way here. Although models suggest the Irish climate might be less suitable for hornets, they still remain a significant risk. Although Asian hornets can sting, they rarely attack humans unprovoked, and sting reports do not seem to have increased in areas they have invaded to date.
From RTÉ News, Asian hornet nest located in Cork city following hunt
The major concerns around hornets are about impacts on honeybees and beekeeping, and on wild insects. Hornets need nectar from plants to give them energy for things like flight, and also feed on ripening fruits causing damage to fruit crops. However, hornets are primarily predators who feed on protein from other insects. They need to feed themselves, but a lot of what they collect is to bring back to feed their developing larvae. Scientists in France who have dissected the stomachs of hornet larvae found both plant pollen and insect remains.
Asian hornets are particularly fond of honeybees. Honeybees have big, active colonies are relatively easy for the hornets to find. Studies using fake bees with and without pheromones have established that hornets sense honeybees using both smell and sight. Smell seems especially important, and scientists are researching more about hornet pheromones which may lead to new options for trapping and controlling them in the future.
Asian honeybees (Apis cerana) are a key food source for the Asian hornet in its native range. However, they have evolved ways to deal with this predator, which means that colony losses of Asian honeybees to the hornet are lower. These honeybees can perform a behaviour called "heat balling" where they surround the hornets, raising the temperature to over 45 degrees which eventually kills the attacker.
We need your consent to load this rte-player contentWe use rte-player to manage extra content that can set cookies on your device and collect data about your activity. Please review their details and accept them to load the content.Manage Preferences
From RTÉ One's Nine News, Dr. Dave O'Leary from UCC describes how he discovered an Asian hornet in a beer garden in Cork
European honeybees (Apis mellifera) are less able to defend themselves, and as a result they are more susceptible to hornet damage. While hornets can directly predate honeybees, the threat of attack can also cause honeybees to stay confined in their colony which can have severe implications for their foraging and survival. Across Europe estimates of colony losses related to hornets are from anywhere between 18 and 80%
But Asian hornets eat a lot more than just honeybees. In France, although honeybees make up a significant proportion of the diet (38%; and even more in urbanized areas), other species such as wasps (19%) and other flies (30%) are also eaten alongside a whole host of other species. A hornet colony can eat about 11kg of insects per year.
Given the importance of pollinating insects for both biodiversity and food production, the Asian hornet is of great concern for pollinators. In addition to the honeybee, the other 99 species of bee in Ireland may also be at risk, but we know a lot less about what the implications of the hornet might be for these species. It may not be all bad news; a study in Spain showed that although hornets caught bumblebees at their nest entrance, the bumblebees were able to escape. All of the bumblebees observed dropped to the ground, and on impact managed to get out of the hornet's grasp.
We need your consent to load this rte-player contentWe use rte-player to manage extra content that can set cookies on your device and collect data about your activity. Please review their details and accept them to load the content.Manage Preferences
From RTÉ Radio 1's Today with Claire Byrne, John Kelly from the National Biodiversity Data Centre on how they're dealing with potential Asian hornet nests
In the same study though, bumblebee colonies in areas with more hornets did not perform as well. Although why this is happening is unclear, it could relate to hornets competing with bumblebees for nectar, or bumblebees changing their behaviour due to the threat of hornet attacks. Indeed, evidence suggests that hornet presence can impact how wild pollinators visit plants, resulting in reduced pollination. However, we know little else and need to learn a lot more about impact of hornets on non-honeybees.
Over the coming years, it is likely that we will see more Asian hornet nests in Ireland. Methods of tracking, monitoring, trapping and eradicating the species are developing all the time, and being a small island we have the opportunity to keep this species out. Although a concern, hornets are not the only risk to our bees and other pollinating insects. We have stronger evidence for the impacts of other threats such as habitat loss and pesticide use, and these shouldn’t be overlooked. Taking a holistic approach to address the threats pollinators face will help to safeguard our honeybees and beekeeping sector, as well as other bee and insect groups.
If you think you have seen an Asian hornet, report it (ideally with a photograph) to the National Biodiversity Data Centre who are monitoring the species in Ireland.
Follow RTÉ Brainstorm on WhatsApp and Instagram for more stories and updates
Dr Dara Stanley is Associate Professor in Applied Entomology in the School of Agriculture and Food Science at UCD. She is a former Research Ireland awardee.
The views expressed here are those of the author and do not represent or reflect the views of RTÉ
