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Understanding the Alarm Around Asian Giant Hornets in the US

Understanding the Alarm Around Asian Giant Hornets in the US

A male Asian giant hornet. Photo: Yasunori Koide/Wikimedia Commons, CC BY-SA 4.0.

Recently, some people spotted Asian giant hornets (Vespa mandarinia) – the largest of all hornets – in the US, prompting widespread fear. These hornets are not native to the US, so observers have also expressed concerns about an invasion, threats to native honeybees and danger to humans.

As it happens, many people came to know of this insect only after media attention on this discovery. And most of what they learnt had to do with how dangerous these insects are and they could be eliminated. Few, if any, commentators were interested in the ecological roles of Asian giant hornets.

The populations of hornets and other wasps have been declining over the years – thanks principally to people destroying hornet nests in earnest. Even many researchers are afraid of hornets.

Hornet stings are very painful and can be lethal, too – but hornets don’t sting unless alarmed.

Hornets are the common name of insects of the genus Vespa, and all members of the insect family Vespidae are called wasps. So all hornets are wasps – but not all wasps are hornets.

Asian giant hornets, known infamously as “murder hornets”, have been in the spotlight ever since people spotted them in Washington state in November 2020. These wasps have a reputation as one of the most venomous insects in the world. They are also the largest hornet species in the world, and thus the largest wasp species as well.

They are native to Asia, so their spread to other parts of the world is a bit of a concern.

However, they are not nearly as murderous as they’re often made out to be. Asian giant hornets feed on spiders and some other insects, and play an important ecological role by controlling pest insect populations. They also pollinate some plants.

Asian giant hornets are colonial insects. A typical hornet colony has queens, workers (sterile females) and drones (males). A colony cycle starts in early spring (March-April), when a queen inseminated in the previous cycle exits hibernation and starts to build a nest. She selects a suitable subterranean location 6-60 cm deep, far from human activity, usually under rotting trees, and erects the nest cell by cell.

A typical nest has 4-7 combs each, with about a thousand cells. By around August, a colony is likely to have 100-400 workers. At this point, the workers emerge in search of food – spiders and honey bees in particular. Adult workers take a stroll and locate honeybee hives following olfactory and visual cues, and mark them with pheromones.

The other workers sense these pheromones, and a whole troupe of these giant insects marches over to slaughter the bees in a few hours. A single hornet is capable of decapitating hundreds of bees every hour, thanks to its strong mandibles. This is where the title of ‘murder’ comes from. Once a hive has been thus decimated, the hornets collect the bee larvae and pupa to feed to their young ones.

Honeybees, especially the Asian honeybees (Apis cerana), have evolved a suite of nest defences to beat back hornet attacks. In the most successful measure, the bees apply animal faeces around the nest’s entrances. Other studies have reported bees working together to form a defensive ball that surrounds a hornet and kills it.

However, the Western honeybee hasn’t yet developed effective defences against Asian giant hornets. This is why there are concerns about Asian giant hornets showing up in the US.

Asian giant hornets are the natural enemies of several insect pests, and are naturally aggressive against their prey. However, while they may get aggressive towards a human near their nest, they are unlikely to do so farther away. Some 50 people on average die from hornet attacks in Asia every year.

Their venom contains an enzyme mixture that acts as a neurotoxin, capable of destroying tissues and even death.

Thus far, there haven’t been specific conservation efforts directed at this species or its habitats. More broadly, less ‘charismatic’ taxa like insects are often excluded from conservation programmes.

An effective way to conserve this species would be with a paradigm that prioritises habitat heterogeneity and ecosystem health – i.e. a ‘habitat approach‘.

Femi E. Benny is a PhD scholar and project associate at Ashoka Trust for Research in Ecology and the Environment, Bengaluru.

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