This week, we started seeing a lot of posts online about a new species of hornet found in Washington. The Asian giant hornet has been dubbed the "Murder Hornet" in headlines across the US, citing brutal honeybee colony destruction and fatal stings. Some headlines warn humans as far as Texas that the Asian giant hornet could arrive there soon. But how scared should you really be about these potential new invasive pests? As it happens with so many of these types of news stories, the threat may be a lot less scary than it sounds. To ease your minds, we spoke with Doug Yanega, Senior Museum Scientist at the University of California's Entomology Research Museum and expert on all things Hymenoptera (the order of insects that includes wasps and bees).
First, the Basics
The Asian giant hornet (Vespa mandarinia) is a type of wasp native to Asia. The queens of the species can reach up to two inches long, making them the world's largest hornet, while the workers are a little smaller. These hornets are known for decimating honeybee colonies and feeding the bees (and bee larvae) to their young. They are also known for their very painful sting, described by some people as feeling like red-hot needles! Despite these characteristics, people in Asia have been living alongside these hornets for a very long time, and have learned to live with them just like any other wasp species. To them, the "murder hornet" is no more worrying than the yellow jackets and paper wasps we see here in North America. Beekeepers in Asia have developed protective devices for their beehives, and Japanese honey bees have even learned how to defend themelves by "cooking" intruding hornets inside a big ball of bees!
The "Invasion"
In August of 2019, a nest of Asian giant hornets was found in British Columbia, Canada. The nest and all of its occupants were promptly destroyed. However, in December, another dead hornet was found in Washington state, near the border with Canada. As far as we know, these were the only Asian giant hornets in North America, but just to be safe, invasive species monitoring will take place during 2020 to make sure no hornets slipped by undetected.
Why Murder Hornets are Not Currently a Threat
Fear not, North America! The likelihood of the specimens found in Canada and Washington being indicators of a larger population of hornets is extremely low. There are many biological factors actively working against the establishment of a new hornet colony.
Life Cycle and Speed of Spread
Unlike many other bugs, Asian giant hornets only reproduce once per year. They mate in the fall, and the fertilized queens then overwinter somewhere safe. In the spring, they emerge to start their own nest with the fertilized eggs from the previous fall. "These insects have one generation a year, with offspring numbering in the 10s," said Yanega. "A single colony would be lucky if a dozen queens from it survived the winter to start colonies the next year. That's nothing compared to an herbivore or scavenger that can produce several thousand offspring per generation, and have several generations a year." This longer life cycle means that at the time the hornet colony in Canada was discovered and destroyed, it would not have had time to produce new queens for the next generation. Even if a fertile queen had escaped, it would probably take years for the species to establish and make its way out of Washington, let alone to the rest of the country. In other words, if you're not in Canada or Washington (and even if you are), you do not have to worry about seeing an Asian giant hornet in North America.
Biological Limitations
Aside from the fact that all of the Asian giant hornets found in North America were destroyed, the species has a lot of biological factors working against its survival. "They need easy access to wild honeybee hives in order to keep their larvae fed," said Yanega. "The biomass needed to sustain a mature hornet colony is enormous. Honeybees are not native here, and we have the option of protecting our managed colonies in addition to reducing our feral populations." Wild honeybee colonies don't happen nearly as often here as they do in the Asian giant hornet's native range, so they would have a very hard time finding enough food to feed their young for even one generation.
Another important limitation facing the hornets is their lack of genetic diversity. If a single fertilized queen arrived in North America, she and her previously-fertilized eggs would be the sole source of genetic material for the entire North American population. "These wasps face an immediate inbreeding bottleneck," said Yanega, "and that won't be doing them any favors at all in terms of their prospects for perpetuation." When a species has a very small number of individuals, it is likely to pass on the same genes to its children over and over again. This makes adaptation to new environments very difficult, because when natural selection occurs, only those individuals with genes best suited for their environment survive. Without a large pool of genetic material to strengthen the species, this single hornet queen would pass on her poorly-adapted genes to all future North American generations, which would drastically limit their ability to reproduce and spread and eventually end in their demise.
Danger of Stings
Any bug with the potential to sting can understandably be scary to humans, but as with most stinging creatures, these hornets do not gain any benefits from stinging you, and will not target humans out of the blue; stings are reserved for protecting themselves or the nest, so you're unlikely to be stung unless you stumble across a nest in the woods or accidentally squish a hornet against a hard surface.
The Asian giant hornet's sting is said to be extremely painful, but what about claims that a single sting can kill? "The response of humans to stings is notoriously variable," said Yanega. "You can give two stings from the same individual insect to the same person and have different symptoms. You can give that same person another sting from a different individual insect and get a different response. You can sting a different person with the same original insect and get a different response, and so on. The point is that responses to stings form a very broad and very messy spectrum." Just like bee stings, it is possible for a human to be allergic to the sting of the Asian giant hornet, which may cause serious symptoms such as anaphylaxis and even death from just one sting. However, if you are not allergic, the chances of having any serious or lasting symptoms from a single sting are highly unlikely. A study of confirmed Asian giant hornet stings in their native range showed a diverse array of symptoms. The vast majority of stings resulted only in pain, redness, and swelling at the sting site, like you might expect from any other insect sting. Occasionally, some bruising and mild bleeding occurred.
The study authors were very clear that severe symptoms were extremely rare, and usually associated with multiple stings, at least more than ten at one time...and all the way up to 100 simultaneous stings! In these cases, some patients did experience shock, organ damage or failure, or even death, but again, it took a high concentration of hornet venom from multiple stings to cause these injuries.
Luckily, the mass-stinging events that may cause more serious symptoms are pretty uncommon. According to Yanega, "Mass stings would certainly be vastly rarer than individual stings, as they would only occur in immediate proximity to a mature colony, which is a very improbable event compared to encountering a single female and being stung by it."
So what about the claims of flesh-melting venom? The study did find that in a few very rare cases, patients developed small necrotic lesions at the sting site, smaller than a dime in size. This means that the toxins in the venom destroyed some of the skin cells around the sting, leaving a small area of dead tissue. While this might leave a small scar, it is far from claims of widespread decaying flesh!
All these symptoms are not unlike those from the stinging insects we are already familiar with here in North America. Stings from native bees and wasps usually result in a painful red welt, but people who are attacked by large numbers of insects at once can develop the more serious symptoms mentioned in the study. In this way, the Asian giant hornet is not that different from bugs we already know (other than the "giant" part!)
Bottom Line
According to Yanega, the Asian giant hornet is "less of a threat here than they are where they are native." The small number of individuals introduced in Canada combined with invasive species containment protocols and inherent biological limitations means that the likelihood of there being any more Asian giant hornets in North America is almost zero!
More damaging than a potential invasion is the panic that has set in across the nation. Insect identification sites are now overrun with pictures of squashed insects that aren't even wasps, let alone hornets; and people are setting out hornet traps that, in the absence of actual hornets, are killing native bees and wasps that are vital to a healthy environment. Native wasps pick thousands of caterpillars and other pests off of your flowers and crops, and without that natural pest control, your gardens and farms would be barren.
At this time, people in the US do not need to be worried about the Asian giant hornet, and should not be attempting to kill anything that looks like it might have a scary stinger! If you still believe you have found an Asian giant hornet, take a picture of it and leave it alone. Your local extension office will be able to tell from the picture if what you found is an Asian giant hornet or one of many lookalikes that are important native insects, and will advise you from there.
For the sake of us bugs and your native ecosystem, please don't swat us!