New study offers hope for invasive hornets control

A 2024 study by Hassal and colleagues indicates promising developments in invasive hornet management and offers valuable insights for reassessing prevailing attitudes towards the warnings of ecological disasters from biological invasions (see details here). The main focus of the study - the yellow-legged hornet (Vespa velutina nigrithorax) - is an invasive species native to Asia, introduced in Europe over 20 years ago. Like other alien hornets, is a voracious predator of honeybees and other wild pollinators. Moreover like other hornets may pose a threat to human health. The study, funded by the European Commission to IUCN, highlights the importance of early detection and rapid eradication as a best option for successful management of this species and biological invasions in general. 

The yellow-legged hornet (Vespa velutina nigrithorax)
Drawing made by Massimiliano Lipperi © European Commission

It took about 10 years since the species was first detected in 2004 in France, before a comprehensive legislation would eventually be launched to address the multifaceted threats of biological invasions, specifically the EU Regulation no. 1143/2014 on invasive alien species. In the meantime, in the absence of adequate response action, the species got established not only in France, but also Italy, Spain, Portugal,  Switzerland, Germany, Belgium, the Netherlands, Luxembourg and Jersey. Moreover, scattered records were reported from Austria, Czechia, Hungary, Ireland, Slovakia, showing that the species may soon further expand its range to other countries.

The adoption of the EU Regulation on IAS has been key to start monitoring and slowing down the spread of this alien hornet. By means of modeling scenarios Hassal and colleagues have shown that the yellow-legged hornet could have spread even further if it hadn't been for the bulwark established by this benchmark legislation. The assessement of the potential extent of invasion by the yellow-legged hornet highlighted that if rapid eradication of early detections had not taken place, the species would have spread more rapidly particularly in Germany and the Netherlands (and in the UK, where early actions have allowed to prevent the spread of the species in the country). Based on environmental suitability for the species establishment and spread, the study also demonstrates the importance of the information collected in nearly real-time through NOTSYS,  the online system where EU Member States are required to notify early detections and rapid eradication measures regarding the yellow-legged hornet, along with any other alien species of Union concern. 

The control of the yellow-legged hornet in Belgium © Photo courtesy of Tim Adriaens

The advantages of a prompt action were further demonstrated by the recent eradication occurred in the United States of the northern giant hornet (Vespa mandarinia), actually the largest hornet in the world. It took only five years to declare this species native to Asia as extinct in the United States, where it was detected in 2019 (see details here).  This was a considerable relief for pollinators, which are already facing several challenges and didn't need another threat to deal with. And it was also an encouraging news for conservation biologists.

Nevertheless, it seems that new problems always arise: another species of alien hornets appeared on the horizon in the old continent. It is the case of the southern giant hornet (Vespa soror) recorded in Spain in 2022 (see details here). This is another aggressive predator originating from Asia, similar in size to the northern giant hornet (the one just eradicated from the United States), and which may have a huge impact on native wildlife, including several groups of invertebrates and well as small vertebrates, e.g. geckos, not to consider the potential health problems to people. Scientists advocating for urgent preventative measures toward new invasions of alien species are often dismissed as modern-day alarmist Cassandra. Despite their accuracy, predictions concerning the impact of invasive alien species - usually informed by documented evidence of ecological damage elsewhere - are often neglected. Yet, the evidence to address this potential new threat to biodiversity and human health as early as possible is unequivocal.

AI generated image (Google 2025)

You may infer from the examples above, it didn't take a Cassandra to foresee the potential consequences of such introductions, and that without prompt action the rapid spread of alien hornets across the entire continent would be inevitable. The Cassandra myth reminds us that scientists warnings of impending disasters are often unpopular and subsequently ignored. Might a more modern approach, such as consulting artificial intelligence (AI), prove more effective? We are just starting to rely on AI for surveillance measures, as shown by the example of the VespAI automated early warning system. It would be interesting to explore the warnings and advices that different AI platforms would provide in reply to the question: "What would happen if the southern giant hornet (Vespa soror) invaded Europe", and "Is it still possible to eradicate the southern giant hornet (Vespa soror) in Europe". The replies are unsurpringly clear and to the point, but also offer a clear window of opportunity ...Will AI eventually be regarded as a modern-day Cassandra, dismissed and ignored as well? 

Alarm for invasive hornet rapidly expanding European range

It was easy to predict the arrive of the Asian hornet in Italy. This invasive alien species native to South-East Asia, was recorded in Europe for the first time in France in 2004, where it was probably introduced accidentally through the horticultural trade. It spread very rapidly across south-western France (at around 100 km per year), and soon reached Spain, Portugal and Belgium. At the time the EEA report on invasive alien species impact was published (December 2012) it was considered likely to arrive soon also in Italy and Great Britain. In fact the news of the arrive of this hornet in Italy was circulated in May 2013, although the new record of the species originates from monitoring activities carried out already in November 2012 (see press release of the University of Turin). This shows that an effective early warning and rapid response system for alien species in Europe is urgently needed, so as to prevent further impacts related to biological invasions.

The Asian hornet © Photo courtesy of Quentin Rome

Invasion risk modelling already suggested that the Asian hornet - Vespa velutina or yellow-legged hornet to be more precise - could spread over a large part of Europe (see article published on Aliens no.31). And there are good reasons to be concerned about the spread of this “giant wasp”. With a body length of 2-3 cm Vespa velutina is in fact a social wasp slightly smaller than the native European hornet Vespa crabro. The head is black with an orange-yellow face. The body is dark brown or black velvety, bordered with a fine yellow band and a single abdominal segment almost entirely yellowy-orange, which makes it difficult to confuse with any other species.

The Asian hornet and its nest © Photo courtesy of Quentin Rome

The Asian hornet is mainly a predator of social wasps and bees, and like the European hornet, it also consumes a wide variety of other insect preys. Honeybees are among the hornet’s main preys, so the Asian hornet is expected to have an economic impact on beekeeping activities. In fact, as a highly effective predator, the new hornet may represent an additional component to the decline of honey bee populations in Europe and its big colonies and diet spectrum suggest that it could have a noticeable impact on biodiversity, including many wild pollinators and other beneficial insects. Otherwise, this species is no more dangerous for humans than the European hornet as in general it is not aggressive. However, its large size, painful sting and noisy flight make it a very frightening insect (and stings may potentially cause life threatening allergic reactions). In general, they will not attack as long as the colonies remain undisturbed, so it is necessary to avoid getting close to their very large nests, which are from 50 to 80 cm in diameter, and might be found in tall trees in urban and rural areas, including garages, sheds, and sometime in holes in walls or in the ground.

The life-cycle of this social insect is very efficient: each colony, initiated by a single individual, can produce several thousands of workers, plus hundreds of males and new founders able to mate and subsequently produce new colonies. Nevertheless research to develop an effective control method for Asian hornets is still in progress. You can find additional information about the species and the relevant management options, as well as the contact details for expert assistance on this link.