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Asian giant hornets are the largest social wasps in the world. Frequently referred to online and in the media as 'murder hornets', sightings of this species in North America, thousands of kilometres from its native range, have been causing concern.
But what threat do these wasps actually pose?
In late 2019, two sightings of Asian giant hornets (Vespa mandarinia) were reported in North America - in British Columbia in September, and Washington State in December.
We don't yet know how far the species might have spread since its arrival on the continent, but beekeepers in particular are worried about the potential impact of this new arrival.
The Asian giant hornet (Vespa mandarinia), also known as the 'murder hornet', is not present in Europe.
For information on the Asian hornet (Vespa velutina) that is found in the UK, Channel Islands and parts of mainland Europe, please see here.
Asian giant hornets are among the world's largest species of wasps. Queens of this species reach over five centimetres long and the slightly smaller workers are about four centimetres long. Giant hornets have an orange head and a dark thorax, and their abdomens are banded yellow, black and brown.
The hornets are seen in areas in Asia from India to Japan. Their range also stretches from some southerly parts of the Russian Far East down into southeast Asia.
Asian giant hornets are a social species that lives in colonies. They typically build their nests underground, such as in abandoned burrows or cavities around tree roots. When they do nest higher up, it is usually no more than two metres above ground.
Like other social wasps, the hornets build a new nest each year, started by a single queen after they emerge from their winter dormancy. The queen will raise broods of female workers and as the colony grows, these wasps take over foraging and nest duties. To ensure the next generation, new queens and males are produced and mate before winter arrives. The males and the current year's colony then die out, and the new queens find a sheltered spot to spend winter in.
Asian giant hornet venom is less toxic than that of other species, but these wasps can inject more per sting. The stinger is long enough to puncture thick, protective clothing, such as the kind normally worn by beekeepers.
This species will defend its nests. What can make them more dangerous than other hornet species is that they will attack as a group, recruiting other members of the colony to join in on the stinging. The quantity of venom they can inject through multiple stings can make them dangerous to young children as well as people with existing health conditions.
It's best for us to avoid their nests, but the hornets do not go out of their way to find humans to sting. They do show more sinister intentions when it comes to honeybees, however.
Asian giant hornets hunt a variety of insects, but their attacks on honeybees are most widely reported. When these wasps attack the bees, they will chew off the head, abdomen and legs, then transport the protein-rich thorax back to their nest - a behaviour similarly seen in some other hornet species.
But the giant hornets have an additional trait: they specialise in eating honeybee broods.
When they invade a honeybee colony, the hornets can enter a 'slaughter phase', where they will serially kill bee after bee. Within a few hours, a small group of hornets can decimate an entire honeybee colony. Once the bee workforce has been depleted, giant hornets will then spend days or weeks predating the honeybee pupae and larvae.
In their native range, Japanese honeybees (Apis cerana japonica) co-evolved with giant hornets. This resulted in the bees developing a defence against their assailants, a clever tactic known as a bee ball.
When a hornet enters a Japanese honeybee nest, the bees gather around the wasp and trap it. They vibrate their flight muscles, raising the temperature and the carbon dioxide level in the ball. The bees can withstand these harsh conditions, but the wasp is effectively suffocated and cooked.
But not all species are so ready for an attack. Much of the world relies on the European honeybee (Apis mellifera) for commercial honey production. But European honeybees don't make bee balls. They will defend their nest by stinging an attacking hornet, but this appears to have no effect.
With the Asian giant hornet recently arriving in North America, beekeepers are concerned about the damage the wasps could cause to the already declining number of European honeybees.
A species of hornet from Asia is also a relatively recent arrival in Europe. Vespa velutina was first sighted in the UK and Channel Islands in 2016. It is commonly known as the Asian hornet.
The similarity in common names of the Asian hornet and the Asian giant hornet has led to some concern and confusion in Europe. To help distinguish these wasps, some experts have suggested the Asian giant hornet be given a new common name.
Asian giant hornets are known by a variety of names across the regions they are established in. They are the 'great sparrow bee' in Japanese, 'giant tiger head bees' in Chinese and 'general officer hornet' in Korean. There is also a former subspecies known as the 'Japanese giant hornet', although this is no longer officially used.
In the media and online, Asian giant hornets are often called murder hornets. While the name is now well known, it is arguably sensationalist - although terrifying nicknames are nothing new.
Wasps are an important part of the ecosystem. Asian giant hornets are not murderous, and negative nicknames like this risks unnecessarily giving rise to a wider dislike of them, as well as to insects more generally.
Some have proposed that, in English, Asian giant hornets be referred to simply as 'giant hornets', while others suggest 'sparrow hornets' or 'sparrow wasps.'
V. velutina, the Asian hornet species in Europe, is increasingly being called the yellow-legged hornet.
The first sighting of the Asian giant hornet in North America was in Nanaimo on Vancouver Island in British Columbia, Canada in September 2019. A nest was discovered and destroyed.
In December 2019, a resident of Blaine in Washington State, USA, reported a large, dead hornet on their property. The Washington State Department of Agriculture confirmed it was an Asian giant hornet.
How the hornets first entered North America isn't certain, although it's thought they may have been accidently transported across the Pacific Ocean in shipping containers.
At the end of May 2020, officials in Washington State confirmed that an Asian giant hornet queen had been found dead on a road near the town of Custer. This find makes it reasonably likely that a colony of the wasps was established in the state in 2019, which would have produced multiple new queens.
Asian giant hornets do not travel far to start new nests, however, and any spread could be limited by the Rocky Mountains and the harsher winter conditions of the prairies further east. Officials will also be tracing and removing nests and trapping individual wasps to prevent the species from spreading.
As the insects hit headlines, reports flooded in from across North America of Asian giant hornet sightings. However, at this stage it appears that the wasps are contained within Washington State and British Columbia.
The 'murder hornet' frenzy has left many worried, but there are a number of wasps native to North America that might be mistaken for an Asian giant hornet.
Bald-faced hornets (Dolichovespula maculata) are native to North America. This species is smaller than the Asian giant hornet and can be distinguished by its black and white colouration.
Woodwasps (Siricidae), also known as horntails, are solitary wasps that are a similar size to giant hornets. However, their bodies are much more cylindrical and horntails are completely harmless to humans. The long, sting-like protrusion from their abdomen is actually an ovipositor.
Cicada killers (Sphecius) are native to the USA and are a similar size to the Asian giant hornet. They are solitary species, preferring to dig nests in open spaces, and use their stings to paralyse cicadas. They place these in their burrow and lay their eggs on them. When the eggs hatch, the larvae feed on the cicada.
The European hornet (Vespa crabro) is well established in the eastern parts of North America. It is similar in size, shape and colour to the Asian giant hornet, but the abdomen is predominantly yellow with minimal dark bands and spots. European hornets typically nest around two metres above the ground in natural cavities such as hollow trees.
If you have seen an Asian giant hornet individual or nest, you should report it to your state or province's agricultural department.