Murder hornets are the largest hornets in the world.
Murder hornets, also known as Asian giant hornets (Vespa mandarinia), are the world’s largest wasps. These hornets naturally occur in Asia, but humans have accidentally introduced them into North America where they pose a threat to native wildlife, as they kill other insects, including smaller wasps and bees.
The name “murder hornet” is widely used online, but it may be sensationalist, according to the Natural History Museum in London. These hornets don’t actively hunt humans but they can kill humans with potent stings if they feel threatened, especially when people are allergic to their venom.
Murder hornets grow up to 2 inches (5.1 centimeters) long, or about the length of a human thumb. They have yellow or orange heads that contrast with their mostly dark brown or black thoraxes — the middle section of their bodies between their heads and abdomens. Their large abdomens have alternating stripes of dark brown or black and yellow or orange, according to the U.S. Department of Agriculture (USDA). Murder hornets have large stingers that are about 0.2 inch (6 millimeters) long.
Murder hornets are omnivores and eat a range of insects, particularly beetles, as well as tree sap and fruit, according to the University of Michigan’s Animal Diversity Web (ADW). The hornets often hunt alone, but they are best known for their coordinated “slaughter” attacks on beehives, where multiple hornets launch an all-out assault on a colony of much smaller bees. During these attacks, up to 20 or more hornets use their mandibles to rip apart the bees guarding the hive and then infiltrate and destroy the rest of the colony.
Murder hornets can kill about 30,000 individuals in a bee colony during a “slaughter” attack. After most of the adult bees are dead, the hornets focus on the bee larvae and pupae — bees’ dormant form between larvae and adults. Murder hornets steal the bee larvae and pupae and take them back to their nest to feed to their own larvae, according to the University of Florida.
Honeybees’ stings can’t penetrate hornets’ thick outer skin, but Japanese honeybees (Apis cerana japonica) have a strategy to defend their colonies against these devastating hornet attacks. The bees swarm an invading hornet in unison and trap it in a tight ball of their combined bodies. They then vibrate their bodies together to heat up the ball until it is about 116 degrees Fahrenheit (47 degrees Celsius), which is hot enough to kill the hornet inside but not too hot to kill the bees, Live Science previously reported. Bees living outside of the murder hornet’s natural range, such as North American native yellow bumblebees (Bombus fervidus) and European honeybees (Apis mellifera) — which aren’t native to North America but help pollinate crops, didn’t evolve alongside the fierce giant hornets and don’t have strategies to defend themselves against murder hornet attacks. This makes the invading hornets more of a threat to them.
Scientists don’t know how murder hornets arrived in North America, but pest response guidelines released by the USDA’s Animal and Plant Health Inspection Service suggest it may be due to the intentional or unintentional illegal importation of live hornets. Murder hornets are consumed throughout Asia for food and used in traditional medicines, and their nests, containing larvae and pupae, are harvested and sold, so it’s possible that some live larvae and pupae were imported and escaped. Another possible route into North America is by murder hornets accidentally stowing away in international freight. Researchers believe that a similar species called Asian hornets, or yellow-legged hornets (Vespa velutina), was accidentally introduced into France when a mated queen made it into international cargo, so this is another possible introduction scenario.
Murder hornets were first seen in North America on Vancouver Island in Canada in August 2019. The hornets were then confirmed to be in the U.S. in December 2019, when the Washington State Department of Agriculture (WSDA) verified two hornet reports near Blaine, Washington, according to the WSDA. Eleven months later, entomologists located and destroyed the first murder hornet nest in Blaine by attaching radio trackers to live hornets they had captured and following them back to their nest, Live Science previously reported.
More murder hornets were reported in Washington and Canada in 2020 and 2021. According to a statement released by the WSDA, one dead hornet found near Marysville, Washington, in June 2021 appeared to be unrelated to any of the previously discovered hornets and was therefore from a separate introduction.