By early April, yellow-legged, or Asian, hornet queens that managed to evade the nest-destroyers from the UK’s National Bee Unit (NBU) last year are just waking up from their long winter hibernation.
Though it is native to the generally much warmer climate of south-east Asia, the yellow-legged hornet is extremely adaptable and has found continental Europe and the UK much to its liking since it arrived in France back in 2004.
A hornet queen spends April building up her reserves by feeding on sugar-rich foods, such as tree sap and nectar. She also constructs the year’s first nest from rotting wood, which she mixes with her saliva to create a hollow, papier-mâché-esque ball. When that’s ready, she’ll lay up to 2,000 eggs, feeding them once they hatch. And that’s when she starts to wreak havoc.
Why are Asian hornets so dangerous?
Yellow-legged hornets feed voraciously on other insects, including domesticated honeybees, to satisfy their brood’s requirement for protein. One nest of larvae can consume up to 11kg of insects, and it’s long been feared – ever since the species was first officially recorded in Britain in 2016 – that the yellow-legged hornet could have a devastating impact not just on honeybees, but also on other pollinators, such as solitary bees, hoverflies and even bumblebees, should it become established.
Peter Kennedy, a research fellow at the University of Exeter who has been studying yellow-legged hornets since 2016, says domestic honeybees are a particular target. “They like to concentrate on aggregations of insects, and a honeybee colony provides the convenience of a supermarket as opposed to visiting lots of local stores,” he says.
In the autumn, Kennedy has observed yellow-legged hornets predating bees at honeypot sites, such as flowering ivy. “They patrol these places and just pick off what they want,” he says. Our native European hornet, in contrast, does feed on honeybees, but is not a specialist hive predator.
But while we know that beekeepers in France have suffered losses averaging 30 per cent of their colonies across the country, the picture for native wild pollinators is less clear. “You’d have hoped that, with hornets being present in France all this time, we’d have a much better handle on the impact they’re having on native species, but in most cases we didn’t have the baseline data to say if numbers have really declined,” says Kennedy.
Kennedy and his colleagues have carried out a study, due to be published this year, in which they analysed the DNA of hornet larvae to identify what the adults have been predating. They found evidence of bumblebees, even though they have also published a study that shows bumblebees – unlike other insects – are often able to escape hornet attacks.
How are Asian hornets being tackled in the UK?
Despite the lack of clarity, the UK authorities are taking the threat of the yellow-legged hornet seriously. Operatives from the NBU investigate any confirmed sightings and trace individual insects back to their nests, which are then destroyed. In 2024, 43 nests were eliminated; in 2023, 72. The fact that numbers declined last year is not seen as consequential – the overall trend, though not well set, is upwards.
The first yellow-legged hornet found in the UK arrived in a consignment of cauliflowers, but the British Beekeepers Association points out that there are various ways in which these insects can get here. They are not just hitchhiking in produce but also on ferries and in caravans, and are even potentially carried by the wind, if it’s blowing in the right direction. According to Kennedy, this is suspected but not certain. “Seven nests found below the White Cliffs of Dover does suggest there was an event that favoured multiple landings,” he says.
Beekeepers on Jersey are on the frontlines of the battle, owing to the island’s location close to the French coast. They identified 262 nests in 2024 and 339 the year before and, according to volunteer John de Carteret, who helped to found the Jersey Asian Hornet Group in 2017, there’s no hope of eradicating the species.
“The policy in Jersey is to go all out to find nests and then destroy them,” he explains. “We can’t eradicate the hornets, though; we can only suppress their numbers. Eradication in our geographical location would be almost impossible.”
The question for British beekeepers and conservationists is whether that is also true of Britain. A paper published in 2024 by scientists at the UK Centre for Ecology & Hydrology (UKCEH) said the species had not yet become established here but would have done had it not been for the coordinated response of the authorities and volunteers.
Kennedy says it’s almost a question of semantics as to whether the species is established or not. “We are right on the cusp of where it might have established,” he adds.
Helen Roy, an ecologist at UKCEH, takes a different view. “As long as the response keeps going in the way it has been, we have every hope to stop it,” she says.
Asian hornets vs European hornets
Successfully distinguishing yellow-legged hornets from European hornets – as well as from other lookalike insects such as the hornet hoverfly – is, of course, key. Thanks to continued work by UKCEH and other organisations to promote awareness of the species, there is a “fantastic level of engagement” with the issue, according to Helen Roy.
“During the month of the Chelsea Flower Show last year, we had something like 20,000 sightings,” she says. Of course, the vast majority of those were not yellow-legged hornets, and this creates a massive workload for the organisation because it has to consider every potential record.
Kennedy and colleagues are addressing this by creating an AI system on a platform known as Vespa.ai. Using a bait station and camera, the system has learned to distinguish the yellow-legged hornet from our native species and from other, similar-looking insects.
“We are confident that it is 99 per cent correct,” Kennedy says. They don’t quite understand how the system knows what it is looking at, but the “shape of the hornet and certain colour patterns are important; the yellow legs are not”.
Nonetheless, this new tech has its limitations. The feeding station and camera attachment have been made using 3D printing, which would be too expensive for a mass rollout. And so far, the system has only been used in a situation where it can connect to wi-fi rather than a mobile 4G signal.
Future invasive species
We have more than 2,000 species in this country that are classed as non-native but the vast majority are harmless. Only 10 per cent are termed invasive, which means they are likely to have an impact, whether environmental, economic or to human health. Such species can be very damaging and there are always more on the horizon – other hornets, such as the oriental hornet, could reach Britain eventually.
According to Helen Roy, the next significant invasive species could be a non-native ant – Argentine ants in London have been shown to survive the winter and could wreak havoc if they get into the broader environment. Globalised trade and travel mean we can never let our guard down when it comes to wildlife.
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Main image: an Asian hornet. Credit: Getty
