Killer horns, also known as Asian giant horns (Vespa mandarinia), is the world’s largest wasp. These horns occur naturally in Asia, but humans have accidentally introduced them to North America, where they pose a threat to native wildlife as they kill other insects, including smaller wasps and bees.
The name “murder horn” is very common online, but it can be sensational, according to the Natural History Museum in London. These horns do not actively hunt humans, but they can kill people with powerful stings if they feel threatened, especially when people are allergic to their venom.
What does the killer horn look like?
Killer horns grow up to 5.1 inches long or about as long as a human thumb. They have yellow or orange heads that contrast with their mostly dark brown or black thorax – the middle part of their bodies between their heads and abdomen. Their large abdomen has alternating streaks of dark brown or black and yellow or orange, according to the U.S. Department of Agriculture (USDA). Killer whores have large stingers that are about 6 millimeters long.
Related: How to tell a ‘killer horn’ from other ugly wasps
What do killer horns eat?
Killer horns are omnivorous and eat a variety of insects, especially beetles, as well as tree sap and fruit, according to the University of Michigan’s Animal Diversity Web (ADW). The horns often hunt alone, but they are best known for their coordinated “slaughter” attacks on beehives, where several horns launch a total attack on a colony of much smaller bees. During these attacks, up to 20 or more horns use their jaws to tear the bees guarding the hive apart, then infiltrate and destroy the rest of the colony.
Killing horns can kill about 30,000 individuals in a bee colony during a “slaughterhouse” attack. After most of the adult bees have died, the horns focus on the bee larvae and pupae – the bees’ dormant form between larvae and adults. Killer horns steal bee larvae and pupae and take them back to their nest to feed their own larvae, according to the University of Florida.
Size: Up to 2 inches (5.1 inches) long
Life: Up to one year (queens)
Preservation status: Not listed
The stings of honeybees cannot penetrate the thick outer skin of the horn, but Japanese honeybees (Apis cerana japonica) have a strategy of defending their colonies against these destructive horn attacks. The bees swarm an invading horn together and catch it in a tight ball of their combined bodies. They then vibrate their bodies together to heat the ball until it is around 116 degrees Fahrenheit (47 degrees Celsius), which is hot enough to kill the horn inside, but not too hot to kill the bees, Live Science reported earlier. Bees that live outside the natural range of the killer horn, such as North American native yellow bumblebees (Hops hot) and European honeybees (Apis mellifera) – which is not native to North America but helps pollinate crops, did not evolve with the violent giant horns and has no strategies to defend itself against killer horn attacks. This makes the invading horns more of a threat to them.
How did killer horns come to the United States?
Researchers do not know how killer horns arrived in North America, but pest control guidelines published by the USDA’s Animal and Plant Health Inspection Service suggest it may be due to intentional or unintentional illegal importation of live horns. Killer whores are consumed throughout Asia for food and used in traditional medicine, and their nests containing larvae and pupae are harvested and sold, so it is possible that some live larvae and pupae were imported and escaped. Another possible route to North America is by murdering horns accidentally bouncing away in international goods. Scientists believe that a similar species called Asian hornets or yellow-legged hornets (Vespa velutina), was accidentally introduced in France when a paired queen made it an international cargo, so this is another possible introductory scenario.
Killing horns were first seen in North America on Vancouver Island in Canada in August 2019. The horn was then confirmed to be in the United States in December 2019, when the Washington State Department of Agriculture (WSDA) verified two horn reports near Blaine, Washington, according to the WSDA. Eleven months later, entomologists located and destroyed the first killer horn nest in Blaine by attaching radiosporers to live horns they had captured and following them back to their nest, Live Science reported earlier.
Several killer horns were reported in Washington and Canada in 2020 and 2021. According to a statement from the WSDA, a dead horn found near Marysville, Washington, in June 2021, was unrelated to any of the previously discovered horns and was therefore from a separate introduction.
Related: Monstrous ‘murder whores’ have reached the United States
Killer horns are social insects that live together in colonies or nests. All killer horn colonies begin in the spring with a paired queen. Queens feed on tree sap while looking for a good place to start a colony – usually a cavity or hollow area near the roots of the trees, according to the University of Florida. The queen creates comb cells by mixing its saliva with wood fibers and laying eggs in them, which then hatch as white larvae.
The queen feeds her larvae with tree sap as well as insect and spider tissue, which she collects near the nest until the larvae mature into pupae and then emerge as adults, according to Oregon State University. This process takes about 40 days. The queen initially produces only non-reproductive female worker horsetails that take over the maintenance of the colony, including expanding the nest and feeding after food, so the queen can focus on laying more and more eggs.
The killer horn taxonomy
Genus and species: Vespa mandarinia
Males and breeding females or queens are born later in the year around the end of October. Males hang out at the entrances to colonies to mate with the new queens as they appear. After one she has mated, she finds a place in the ground to spend the winter and remains inactive until next season, when she will appear and establish a new colony, according to the University of Florida.
The queen of the original colony dies around mid-November, and the colony fails shortly after without a queen to get more workers. Murder horn queens live up to a year to give them enough time to establish and lead their colonies. The working horn only lives from spring to winter, and male horns live even shorter, usually dying after mating with a queen in the fall, according to ADW.
Related: Bees defeat relatives from the ‘murder horn’ with their mouths
Are killer horns dangerous to humans?
Killer horns can sting people trying to pick them up, and will also sting when defending their nest or a beehive they attack, according to the WSDA. Their stings are more dangerous than native wasps and bees as they have longer stingers, deliver a larger dose of venom and can sting repeatedly.
Killer horns do not usually pose a threat to humans, but their stings can cause a severe allergic reaction, called anaphylaxis, in some people that resembles other stinging wasps, according to Oregon State University. People suffering from a severe allergic reaction can be killed without treatment. In rare cases, a large number of killer horn stings can also cause people who are not allergic to the stings to suffer organ failure and die. According to a 2007 study published in the journal Clinical Toxicology, killer horns kill an estimated 30 to 50 people each year in Japan.
The WSDA recommends that people exercise extreme caution if they are near killer horns, and people who are allergic to bee or wasp stings should never approach them. If you encounter a killer horn, stay calm and slowly leave the area, or if you are driving, stop the car slowly and open all windows. If you encounter multiple horns at once, the WSDA recommends that you run away or dive into a dense brush for better protection against attack. A person should seek medical attention immediately if they are stung several times and call the emergency center if they experience a severe or anaphylactic reaction, according to the Washington State Department of Health and the WSDA.
- The Washington State Department of Health website offers more information on bee and wasp stings.
- National Geographic has a short video on YouTube of Japanese honey bees defending themselves against a killer horn attack.
- The WSDA offers more information on killer horns in the United States and how to report an observation.