Professional Pest Controller Magazine Issue 98

26 February 2020

Spring Queening: On the trail of Asian hornets in Guernsey

Pest control | PPC98 March 2020

Elliott Rose-King, from BPCA Consultant Member Bounty Consultancy Services, talks to PPC about a recent fact-finding visit to The Agriculture, Countryside and Landscape Management Services (ACLMS) team at the States of Guernsey Government.


  • Asian hornets were first confirmed in Guernsey and Sark in July 2017
  • Predation of honey bees is at its peak around mid to late summer, and continues until the very end of an Asian hornet nest’s life cycle
  • ‘Spring Queening’ saw traps distributed to volunteers across Guernsey, Sark and Jethou, aiming to catch queens before they start building nests
  • The programme has improved understanding of how Asian hornets behave, and how best to track and treat them
  • Pest technicians should consider how, or if, these approaches could be applied to areas across mainland UK where Asian hornets have already established.


Since the first sightings in 2017, Guernsey has been front and centre in facing the threat of Vespa velutina (the Asian hornet).

After the Asian hornet’s arrival in Europe in 2004, when it was accidentally imported to France on some pottery, Asian hornets have spread rapidly.

In just 10 years they’ve reached as far as Spain, Portugal, Italy and Germany!

The presence of Asian hornets poses a threat to both humans and wildlife, but the most notable threat is to pollinating insects, especially Europe’s honey bees (Apis mellifera).

Unlike their Asian counterparts (such as Apis cerana), they have not adapted to defend themselves from predation by ‘hawking’ from Asian hornets and can make up most of an Asian hornet’s diet in our local ecosystems.

Following sightings in Alderney and Jersey in 2016, Asian hornets were confirmed in Guernsey and Sark soon after, in July 2017.

Due to the small and relatively isolated nature of Guernsey, they have the potential to cause significant damage to the island’s wildlife and sensitive ecosystem.

Some of this damage could even become irreversible and cause local extinctions of insects they prey upon, as there is no way for these species to naturally spread back to and repopulate the island.

The States of Guernsey Agriculture, Countryside and Land Management Services’ (ACLMS) implementation of a three-year Asian Hornet Strategy (2019-2021) led to the establishment of an Asian Hornet Team (AHT), to mitigate these impacts.

Their work has included tracking and treating Asian hornet nests and spreading awareness of the situation across the island.

Most of this work is experimental, based on research, information sharing and past experience with Asian hornets across Europe.

This means that the AHT is still in the process of learning what methods work best in Guernsey, and is always evaluating the team’s relative merits and adapting methods as projects continue.

On our visit to Guernsey we met the AHT and other ACLMS staff, to share information, find out about Asian hornets, and the current state of their population in Guernsey.

We discovered what is being done to control their numbers and how this can be adapted for the (highly likely) arrival of Asian hornets to the UK mainland in the near future.

Most of this work is experimental, based on research, information sharing and past experience with Asian hornets across Europe.

Elliott Rose-King, Bounty Consultancy Services

What are Asian Hornets?

Asian hornets (Vespa velutina) are actually smaller than our native European hornets (Vespa crabro).

There is a common misconception that they are larger (mostly due to confusion with the 45mm Asian giant hornet, Vespa mandarinia). However they actually measure between 20-32mm, compared with the European hornet’s 25-35mm.

As seen in the main image, the Asian hornet is characterised by yellow-tipped legs and predominantly black body, with the notable exception of the orange band on the fourth section of the abdomen.

Studies since their arrival in France have shown that Asian hornets prefer to predate social Hymenoptera (such as wasps and bees) when looking for protein to feed their larvae.

In all environments studied in France (urban, agricultural and woodland) this mainly consisted of honey bees.

Honey bees make up an average of 37% of their diet, closely followed by flies at 34% and then wasps at 18%. However, in urban environments honey bees were found to make up to 66% of their diet!

This presents a danger to honey bees in Europe, especially as they have not adapted to defend themselves from Asian hornets.

The Asian hornet life cycle, in our climate, tends to begin as early as March (in temperatures above 10°C), when the queen emerges from hibernation and will find a site for the primary nest.

Towards the middle or end of spring the first workers will start to emerge and the rate at which the nest is expanded (and further workers are produced) starts to increase.

It is at this point that gathering of protein to feed the larvae (which heavily relies on the predation of honey bees) increases and will continue to do so as the nest grows.

The Asian hornet life cycle, in our climate, tends to begin as early as March (in temperatures above 10°C), when the queen emerges from hibernation and will find a site for the primary nest.

Elliott Rose-King, Bounty Consultancy Services

Predation increases until the peak of protein feeding, around mid to late summer, and continues until the very end of a nest’s life cycle, when males are produced and up to several hundred queens are created to hibernate over winter.

This can be as late as mid-November.

Usually around the middle of the summer a larger, secondary nest will be created, to accommodate for the growing number of hornets.

This can be made from the queen’s smaller primary nest or in a new location, if the primary nest was too exposed or space was limited.

Some populations have even been found to establish satellite nests, that continue to work together with the original nest!

At this peak an established nest can contain thousands of hornets, which presents a clear threat to our native honey bees and other insect species.

Asian hornets can also pose a threat to humans through characteristics such as their alarm pheromone, which is contained within their venom.

This means once a perceived intruder near the nest has been stung, other workers are immediately drawn to the alarm pheromone to join the attack on the intruder.

The reaction to the alarm pheromone from hornets in the nest can be very severe, and as nests have been found underground, in low brambles, on buildings and in the tops of tall trees they can be very dangerous to anyone unprepared, or unaware, nearby.

This has posed a notable risk to hedge cutters and other landscapers recently, as their activities have the potential to unintentionally disturb nests in areas where Asian hornets have established.

In addition to this, the sting of an Asian hornet can be up to 6mm long!

This means they are likely to be able to sting through a normal bee suit, especially if the wearer does not have layers on underneath.

As a result, the AHT has had to take extra safety measures, such as the use of specialised Asian hornet protective suits.

Guernsey’s ‘Spring Queening’ trapping programme

Guernsey’s efforts to manage the spread of Asian hornets in 2019 began at the very start of the season with the ‘Spring Queening’ programme.

For this process, traps were distributed to approved volunteers (these were mostly householders or farmers) across Guernsey and to the neighbouring islands of Sark and Jethou.

This stage of the programme aims to catch queens while foraging, before they start building nests.

As stated on the Guernsey Government Asian hornet website the logic behind this is that each queen caught prevents a nest being built, that could potentially contain thousands of hornets later in the season.

spring-queening-asian-hornet-bpca-bounty 3

The traps used were distributed with a harmless liquid bait, based on natural sugars, with an added component to deter honey bees.

The traps were also modified to contain sponges to reduce insects drowning in the trap and 6mm holes (specifically sized to prevent the escape of Asian hornet workers and queens) to allow wasps and other non-target insects to escape.

After research into the known foraging ranges of newly emerged queens, it was decided by the AHT to try and distribute traps every 500m across the islands, which resulted in 260 traps in total being set up.

As literature states foraging queens emerge from the end of March until the end of May (when workers start to be found and the queens are no longer actively foraging) at which time the volunteers were to take their traps down for collection by the AHT.

Once the volunteers have set up the traps, they are asked to monitor them daily, topping up the bait and releasing non-target insects as necessary.

If a suspected hornet is caught the AHT is contacted to make an identification.

20 of the 260 traps were monitored directly by the AHT project coordinator as part of a pilot study to determine the impact the trapping has on non-target insects.

This will enable the AHT to evaluate what else the traps are catching, as it is important that the trapping programme does not cause significant harm to beneficial pollinating insects.

Track! Don’t trample!

Later in the season the AHT asks the volunteers to take the traps down to avoid trapping increased numbers of non-target insects.

Although, some traps have been kept up and are monitored regularly by beekeepers.

If a suspected or confirmed Asian hornet sighting occurs the AHT will track the worker hornets back to the nest, which can involve traps being placed again to catch the hornets so they can be tracked.

Initially the tracking of hornets is done visually, to find the nest.

This can be challenging especially as the Guernsey AHT’s experience so far has shown that, unlike European hornets, Asian hornets seem to fly via markers in the landscape, rather than in a direct line.

If necessary, additional traps will be added and additional volunteers sometimes join the tracking process to narrow down the nest location.

In some difficult circumstances a tracker and radio tracking antennae are used to manually track a hornet back to the nest.

The small tracker has to be manually attached to a captured hornet, so this is a difficult and delicate process!

Later in the season the AHT asks the volunteers to take the traps down to avoid trapping increased numbers of non-target insects.

Elliott Rose-King, Bounty Consultancy Services

To increase awareness of the importance of alerting the appropriate authorities and preventing people from just squashing any Asian hornets they spot, the AHT had a campaign with the slogan ‘Track! Don’t Trample!’ for this season.

This campaign was initially introduced in 2018 and remains an important way for the AHT to engage with the public.

The AHT aims for this campaign to reduce the number of non-target insects that are killed and to get the public to send photos of suspected hornets, their location and (if possible) note the direction they are flying in.

By doing this the AHT can then track more hornets back to their nests.

The ‘Track! Don’t Trample!’ literature includes illustrations to help people reduce the likelihood of them misidentifying a non-target insect as an Asian hornet (most commonly this happens to the ‘Hornet mimic hoverfly’, Volucella zonaria).

Once the hornet has been tracked to the nest, the nest is treated by a competent, qualified, pest controller.

Not only is it important that the pest controller is competent to ensure the treatment is correctly carried out, it is also important that they are aware of the dangers Asian hornets pose.

Once the treatment is complete and the pesticide has had time to work the nest is observed to make sure no worker hornets are visiting from a satellite nest.

If this is the case, the satellite nest is then tracked down and also treated.

Treated nests are removed as soon as possible after this full treatment process is complete.

Removed nests are then frozen for 24 hours to ensure all of the hornets, including sealed pupae, are killed.

The nests can then be safely and carefully examined as they can reveal important information, such as when the new queens are being reared, before they are destroyed.

If a satellite nest exists and is not treated the queen can continue to produce more workers and cause harm to the environment.

They can even create another nest or recolonise the treated nest if it is not removed!

Even a nest that only contains workers (if the queen has died from the treatment) can continue to create or recolonise nests and survive for the rest of the season.

While this means they will not be able to produce eggs, they will still pose a threat to humans and wildlife if they are not removed.

spring-queening-asian-hornet-bpca-bounty 2

Results so far

The AHT has already been able to evaluate the success of other methods they’ve attempted and have used this to eliminate some less successful methods, such as thermal imaging or using protein baits.

Data on the sizes of hornets they have collected has allowed the AHT to create specifically sized holes in the traps that allow non-targets to escape, while keeping the hornets trapped.

The experience with tracking hornets and treating hornet nests has also allowed the team to improve our understanding of how Asian hornets behave in our native environments, and how we can best track and treat their nests.

It remains to be seen how successful Guernsey’s approach to containing invasive Asian hornets through spring queening and tracking programme is, although previous results from Alderney (where spring queening was attempted last year) and early signs from this year have been promising!

Since the most recent update, 10 queens had been captured (or found) during spring queening on Guernsey, 11 on Sark, one on Jethou and seven on Alderney.

Outside of spring queening, only 26 confirmed Asian hornets have been sighted in Guernsey (this is out of 237 total reports of potential sightings and includes the islands of Sark and Jethou).

In comparison, 55 confirmed sightings occurred in 2018. Similarly, in 2018 eight secondary nests were found (and treated) in Guernsey, but so far this year there has only been one report of a secondary nest (one primary nest was also found and treated).

We spoke to many different people while we were on the island (from the staff at our accommodation to shopkeepers) and they were all aware of the situation as well as the non-alarmist and factual nature of the media campaign put out by the AHT.

We could see from the press releases and newspaper articles we were shown on our visit that responsible coverage, especially from the local press and on social media, has been integral to spreading the right messages.

It’s also clear from the experience in Guernsey that we really need to increase awareness of Asian hornets and their danger in the UK, as well as increasing our preparedness for their arrival.

If we do not do this we can easily be caught off guard, unaware of how to treat them safely, leading to incorrect treatments.

This could not only spread the hornets out more to satellite nests but could also endanger pest controllers and the general public.

The future

spring-queening-asian-hornet-bpca-bounty soc med

It will not be possible to gauge the success of Guernsey’s Spring Queening programme until the autumn.

AHT reported that they were actively tracking worker Asian hornets to locate the first secondary nest of the season.

However, this follows a 10-week absence of any confirmed Asian hornet sightings during June, July and August!

The indications are that spring queening may have been successful in controlling the spread of hornets so far this year.

It would be really interesting to consider how, or if, these approaches could be applied to areas where Asian hornets have already established or if they could be scaled up and adapted to work for somewhere the size of mainland UK.

Whatever the outcome, we have returned to the UK with a much greater awareness of what we will have to face and how much the UK needs to prepare.

The entire experience has really highlighted how much we could all benefit from working together on this issue as we all go forward into the future, and how this sort of information sharing UK-wide could really help us understand Asian hornets and how to deal with them, when they almost inevitably arrive here in the near future.

  • The Asian Hornet Handbook2
    Sarah Bunker (2019)
  • The Asian Hornet
    Professor Stephen Martin (2017)
  • Monitoring and control modalities of a honey bee predator, the yellow-legged hornet Vespa velutina nigrithorax (Hymenoptera: Vespidae)
    Quentin Rome, Adrien Perrard, Franck Muller and Claire Villemant (2011).
  • Francis Russell for the sample Asian hornet
  • Guernsey AHT for providing pictures from their local expert photographer; taking the time to take us to a site with a trap and showing us the onsite trap checking process
  • Linda Archard (Principal Analyst and Crop Biologist at ACLMS) for demonstrating and explaining the sample nest
  • Guernsey ACLMS for being so welcoming and providing us with so much information and experience on our visit.
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