Asian hornets are exceptionally aggressive predators of our native insects but they pose no greater threat to human health than our native wasps and hornets, writes Ann Chilcott, Scottish Expert Beemaster.
Around the world, there are 22 species of hornets (Vespa) and 23 species of wasps (Vespula) from the order hymenoptera. All hornet species are found in Asia but the one we are concerned with is Vespa velutina nigrothorax which made its way from China to Europe undetected till first spotted in France in 2004. One or two mated queens may have been transported in a consignment of Chinese pottery, and they may also have arrived and gained a toe-hold some time prior to being first noticed.
So, a couple of hibernating fertilised queens were able to start entirely new successful colonies in France despite the fact that their female offspring would probably mate with their brothers which could reduce genetic diversity and cause some loss of vigour. Inbreeding usually results in the failure of populations but not always, and hymenoptera, such as honey bees, and hornets, engage in multiple mating with different males and so produce offspring with a mixture of gene combinations. Wasps and ants mate usually with one male and it is thought that the same is true for Asian hornets, but not always (1).
Since 2004, the population of Asian hornets has risen to over 50,000 nests in France and they have spread to Spain, Portugal, Italy, Germany, Switzerland and Belgium. French beekeepers have experienced 30% honey bee colony losses due to this insect. The Asian hornet can travel up to 60km/year and it is estimated that the UK could be colonised within 10 years if the advance cannot be halted. They can be transported in fruit, vegetables, cut flowers, soil, wood and wood products, and man- made products making an easy entry at our sea ports and airports. Mated queens may fly across the channel.
One of the problems is that our European bees have not adapted to live alongside the Asian hornet and have not yet acquired all the defensive skills of their Asian counterparts to deal effectively with these cunning hawking hunters.
Asian, or Eastern honey bees adopt a couple of strategies which include: coming out of the hive entrance in large numbers and forming a “bee-carpet” which can deter the hornet; by heat balling the hornet through staying inside the hive and luring in the hornet and then surrounding it in large numbers whilst raising its temperature to lethal levels; bees in the wild living on hanging combs in the open give a visual warning signal by wobbling their abdomens in synchrony thus creating a shimmering effect which can act as a deterrent.
The actual damage to honey bees and other important pollinators, such as hoverflies and wasps, in Europe is caused by the hornet’s need for protein, firstly, early in the season around April after the fertilised queen comes out of winter hibernation and needs to feed the developing larvae in the small embryo nest which houses the first female worker hornets, and then around August when the secondary nest is constructed, and male rearing begins. Protein comes from the bodies of honey bees hawked at the hive entrance and caught by the hornet’s front legs on their return from foraging trips. Sugar is extracted by licking the haemolymph which is the bee equivalent of blood. Everything is then discarded by the hornet apart from the thorax, containing the juicy protein-rich flight muscles, which is carried back to the nest and fashioned into “meatballs” to feed to the larvae.
Since hornets, like wasps, obtain most sugars from larval secretions they are driven to obtain protein and so are not so likely to be attracted to sugar based traps once the first larvae appear. They differ from wasps in that Asian hornet queens relocate their nests and build enormous structures higher up, in tall trees mostly, around August when they will raise males and queens, and so the quest for protein continues, whereas the wasp completes brood rearing by late summer and craves sugar having no offspring to supply it. After mating fertilised queens prepare for winter hibernation whilst the female workers and males all die.
Apart from reducing honey bee numbers by targeting returning foragers, Asian hornets affect bee behaviour by causing them to stop foraging and to stay indoors. Vital nectar and pollen stores are not collected, the larvae are not fed properly, hive temperature reduces, colony moral is lowered, the colony weakens and fails to thrive leading to collapse and death. Hornets may go into weak poorly defended hives and destroy the larvae. In Asia, sometimes the honey bee colonies abscond from their hives to avoid the hornets.
The first confirmed UK sighting of the Asian hornet was in September 2016 in Tetbury, Gloucester where a nest was destroyed by bee inspectors from the National Bee Unit (NBU). A month later in Somerset, forty miles away, another hornet was reported but this one was desiccated and little information was obtainable. Also, that year there were confirmed sightings on Channel Islands, Alderney and Jersey. The following year in 2017 a queen recently out of hibernation was found flying round a retail warehouse in central Scotland, and more were found on Jersey. Others were found in Woolacombe Devon by beekeeper Martyn Hocking last year. In early April of this year it was reported that a dead Asian hornet was found on a cauliflower in Bury, Lancashire and traced back to Boston Lincolnshire. We wait with bated breath to see what happens this year.
So, what can we do about this serious threat to UK beekeeping, commercial pollination and beekeeping businesses, native plant pollinators, and our economy?
Firstly, we need to be able to identify an Asian hornet and that may be easier said than done given that most likely we will first notice them flying which is quite different from looking at their photographs and studying details on an ID chart. Martyn Hocking explains well his experience of finding hornets in his Devon apiary in his YouTube presentation. He also illustrates how Government inspectors may become overwhelmed should Asian hornet numbers vastly increase in the UK leaving, for example, the beekeeping public to deal with nest eradications which will necessitate specialist health and safety training.
The main Asian hornet’s identifying features are: small 3cm size compared with larger 4cm European hornet (Vespa crabro); black thorax and most of body; yellow/orange band on the fourth abdominal segment and a yellow face. For more information, visit the Non-Native Species Secretariat (NNSS) for useful identification sheets.
An app can be downloaded for iPhones and android phones, Asian Hornet Watch – Apps on Google Play which will help you identify Asian hornets and you must then report your finding to: firstname.lastname@example.org.
This insect has few natural predators but is preyed upon by the Eurasian jay, honey badger and honey buzzards which are not found in the UK. So, what can we do to eliminate Asian hornets over here? Current advice is for the public not to destroy nests but to immediately contact the NNSS on sighting a hornet, or nest. They will arrange for bee inspectors from the NBU to deal with the nest destruction which is done by injecting insecticides into the nest. If the situation changes and the hornets become firmly established then the policy will change along with the numbers of people required to deal with nest destruction.
Destroying the large late summer nests containing the male and female hornets, before the females become mated, is a means of keeping populations down but relies on detecting nests which are usually high up in trees. The best way of finding them is to look upwards for nests from July, and to follow the flight paths of hornets for directions to the nests. In the autumn, Asian wasps may be attracted to ivy which secretes copious nectar with a high glucose content so spend some time looking on ivy flowers then.
You may wonder why I haven’t suggested destroying the early embryo nests in spring. This is because of a strategy called usurpation whereby, if these nests are destroyed queen hornets, instead of rebuilding them, will invade another nest and kill its queen and take over that nest. This can result in increased strength of the surviving colonies, according to wasp studies carried out in New Zealand, and therefore this practice promotes Asian hornet populations rather than reduces them.
Hornet traps are not good unless target-specific because hundreds of important pollinators including moths fall victim otherwise. Scientists are working on creating attractant pheromone lures and traps for Asian hornets only. Beekeepers can place a physical barrier in the form of a wooden trap (“Api shield”) under the hive floor to deter hornets who enter through holes then become trapped having no access to the brood nest. Beekeepers can maintain strong colonies and keep the hive entrances small. Potential biological controls in the form of nematodes, which are specialist parasites of social insects, have been studied in New Zealand on wasps but the latter were very resilient to infection and may not be very effective against Asian hornets either.
For now, the best thing that the public can do is become competent in identifying the Asian hornet whilst being vigilant and observant during day to day activities, whether a beekeeper or not. Look carefully at any strange insects lurking amongst that old sacking in your shed in winter and report suspicious findings immediately.
References: (1) Martin, S.J. 2017. The Asian Hornet. The International Bee Research Association & Northern Bee Books.
This article was written exclusively for Smallholder magazine by Ann Chilcott, Scottish Expert Beemaster.