Why Asian hornets are bad news for British bees
Asian hornets have been seens across Britain in the last two years. Hornets are the largest members of the wasp family Vespidae and this predatory species could have a devastating impact on British honeybees.
Dr Gavin Broad, a wasp expert at the Museum, explains why British beekeepers are concerned about the Asian hornet (Vespa velutina), a species that first arrived in Britain in 2016.
Report Asian hornet sightings
Asian hornets are an invasive non-native species in Britain and pose a threat to native wildlife, especially honeybees.
Most reported sightings turn out to not be the Asian hornet but it can clearly arrive an establish nests. Please report any possible sightings of these insects.
The non-native Asian or yellow-legged hornet is an invasive species in Britain as their spread could negatively affect the wildlife already living here.
'The issue is that they eat honeybees,' explains Gavin. 'They are specialised honeybee predators and beekeepers are concerned.
'The hornets raid honeybee hives by sitting outside them and capturing workers as they go in and out. They chop them up and feed the thorax to their young.'
The Department for Environment, Food and Rural Affairs (DEFRA) is trying to prevent a nationwide Asian hornet invasion, currently through eradication of individuals and nests. But if the species becomes established in the UK, it is likely there is very little that could be done about it.
Asian hornets were first introduced to Europe when they arrived in France in 2004, thought to have been unknowingly transported in cargo. From there they rapidly spread with numerous sightings of the hornets across Western Europe.
Gavin says, 'At the moment we're hoping people notice the nests early enough. Three nests have been destroyed in Britain, but they'd probably do quite well if they got established.
'It's a distinctive enough species that people notice it - but it only takes one queen for them to make it.'
There are concerns that the Asian hornet is now becoming established in Britain after they were spotted in two locations at opposite ends of England, in the town of Liskeard in Cornwall and in Hull, within a few days of each other.
Where have Asian hornets been found?
Asian hornets are relatively new to Britain, only being spotted here for the first time in the small town of Tetbury, in Gloucestershire in 2016. A nest was found and removed by the National Bee Unit.
There have been isolated sightings of the insects across the UK since then, in Greater Manchester, North Somerset, Devon, Cornwall and Hull. Individuals have also been identified on the Channel Islands of Jersey and Alderney.
Hornets are the largest social wasps and build paper nests to house a colony of up to a thousand workers. As an invasive species, the Asian hornet nests that have been found in Britain have been destroyed - in Gloucestershire, Devon and Cornwall.
Gavin says, 'The Asian hornet typically builds its nest in the open - they often build on tree branches in the foliage. The nest is patterned, which probably helps to disguise it among the leaves.'
This species is active between April and November, with a peak in August and September.
'Asian hornets occur all the way up to the Himalayas, all the way through to Borneo. They've been described as different subspecies in different areas, with different colour patterns,' explains Gavin. 'The ones that are in Europe now are from China.
'Ours probably came from the temperate part of their range, so they're used to winters.'
How to identify an Asian hornet
Hornets are grouped within the genus Vespa. They have larger heads in relation to their body size compared to other wasps, and the structure of the head is slightly different. Their colonies also grow to smaller masses than other social wasps.
'They're much darker than any British hornets and social wasps. They look almost black,' says Gavin.
'The abdomen has really dark patches covering most of the first half and then it gets a bit yellow - it's quite a distinctive colour pattern.'
Asian hornets are also sometimes referred to as yellow-legged hornets owing to legs that transition from brown to yellow at the ends. They also have an orange face.
Asian hornet queens reach up to three centimetres in length and workers around 2.5 centimetres.
Asian hornet lookalikes
There are more than 7,000 species of wasp living in the UK, and a few of them are sometimes mistaken for the invasive Asian hornet.
The European hornet is native to Britain and is slightly larger than the invaders. Queens of this species typically reach 3.5 centimetres long and the workers up to around three centimetres.
They have lighter bodies than Asian hornets and more yellow colouring on the abdomen. The native hornet normally nests in cavities such as tree trunks and badger holes. This species also captures honeybees, but it does not do so habitually.
Compared to other wasp species, European hornets tend to be quite docile.
The median wasp (Dolichovespula media) is the largest non-hornet wasp native to Britain. They have yellow markings on their thorax, unlike the invasive hornet, as well as more extensive yellow on the abdomen.
This species is another recent arrival, first recorded in Britain in the 1980s. They are found spread across southern England and scattered northwards.
The giant woodwasp (Urocerus gigas) is much larger than the Asian hornet, reaching 4.5 centimetres long. Woodwasps are also known as horntails, owing to the females' long, sting-like ovipositor. But these insects are gentle giants and are completely harmless to humans.
The giant woodwasp has yellow antennae, legs and abdomen, which also features a thick black band. These insects have a cylindrical body, rather than having a thin waist like the Asian hornet.
Hornet mimic hoverflies (Volucella zonaria) are the largest hoverfly species in Britain, reaching two centimetres long. Also known as belted hoverflies, they are covered in a light and dark striped pattern that makes them look similar to a hornet to help defend them against predators - although they are completely harmless.
These hoverflies can be distinguished from hornets from their much larger eyes and lack of a sting. They also only have one pair of wings, rather than two like wasps and hornets.
The Asian giant hornet (Vespa mandarinia) hasn't yet reached Europe, although it is sometimes confused with the yellow-legged hornet.
These are much larger wasps than the Asian hornet in Britain. Workers grow to around 4.5 centimetres long and the queens up to 5.5 centimetres. They are also specialised honeybee hunters - but they use far more brutal tactics. Asian giant hornets capture worker bees until the workforce is depleted. They then enter the hive and take all of the honeybee larvae too.
How to get rid of Asian hornets
It would be almost impossible to halt the spread of Asian hornets if they establish permanent populations in the UK. DEFRA is attempting to control their spread by asking the public to report any possible sighting of the insects so that they can be removed.
Sightings and images of the hornet found can also be submitted directly to the Biological Records Centre (BRC) through an online form.
A sting from an Asian hornet is no worse than other British wasps and bees. It will hurt and throb for a few hours and then die down. But as with any venom there is a risk of anaphylaxis - an extreme allergic reaction that can be fatal.
If an active Asian hornet's nest is found, it should not be disturbed. Individual hornets and nests should be reported to be dealt with by The National Bee Unit.