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  • Charluz M. Arocho Rosario

Murder Hornets? Think again!

Updated: Sep 15

By Charluz M. Arocho Rosario


Mild to near panic has been caused by the misinformation spreading on social media about the ‘Murder Hornet’; a misnomer designed to instill fear, of a wasp appearing on the covers of the media in past weeks. But what are they, really? Among the common names are Asian giant hornet, Japanese hornet, or Giant sparrow bee but its scientific name is Vespa mandarinia and it is the largest hornet in the world. The species generally ranges from the subtropical to moderate temperate zones of Asia and is most common in Japan. 

Photo Credit: USDA APHIS [USDA Photo by Hanna Royals]


Native to Asia, an adult “murder hornet” can measure up to 2 inches from head to the tip of the abdomen and 3 inches from one point of the wing to the other, but queens can be bigger.  A predator of bees, the wasps have two attack phases;  Hunting and Slaughter. First, they go through the hunting phase where they have a seasonal predation behavior observed in summer (June-August). During this period, individual hornets attack honey bees, and decapitate worker bees making a “meatball” with the bee's thorax that is fed to the wasp larvae. The second phase, the slaughter phase occurs in the late summer or early fall (September-November) when V. mandarinia exhibits group predation behavior. where hornets capture and kill honeybees (or any other insects) as the hornets take over the hive and now vigorously defendtheir new colony.


 Asian giant hornet simple Id [Photo credit:Washington State Department of Agriculture]


 “Meatball” with bee thorax [Photo credit: T. McFall]


The first detection of a colony of V. espa mandarinia in the U.S. was in Nanaimo, Vancouver Island on September 18th, 2019. In this case, this particular colony was eradicated; but a single dead hornet was found in Blain, Washington on December 8th, 2019. According to the Washington State Department of Agriculture, there may be more colonies and the area is under surveillance. So far, no specimen has been found by authorities in the tropical island of Puerto Rico.


For beekeepers, the arrival of V. mandarinia is an additional stressor since they are currently facing an ectoparasite in the hives, the varroa mite. The varroa mite affects the development of the larvae and causes economic losses in the beekeeping industry. Beekeepers must be aware of the threat from the hornet especially in the slaughter phase since this is the period when the hornets finds a target bee colony. When this target colony is found, the hornets emit an odor trail to call the rest of the hornets around. Mostly the males of V. mandarinia during the fall consume fruiting bodies of Protubera nipponica (fungus) and both sex hornets occasionally feed on banana flowers, camellia, porcelain berry or fennel, the odor trail they emit to call the hornets to resemble volatiles from fermenting sugars (Matsuura 1984). A swarm of hornets can destroy a beekeeper’s colony of hives. Asian bees are adapted to defend the hive by creating a ball of buzzing worker bees which causes the temperature to rise to 45.9C and raising carbon dioxide levels which the hornets cannot tolerate and die. American bees, however, do not exhibit this behavior and are thus susceptible to attacks.


The V. mandarinia does not sting humans unless threatened because they are defending themselves or their nest. The mass attacks are rare, but in extreme cases can cripple the victim. In humans, a sting of this hornet is painful, and in extreme instances can cause anaphylactic shock, an allergic reaction to the insect bite that can lead to death if it is not treated rapidly, as well localized tissue death, known as necrosis, or even cardiac failure. Correct identification of the presence of the hornet is imperative before taking action. Some recommendations on how to deal with this species can be found on the USDA’s pest control guidelines.


If you wanna know more about murder hornets, other resources that might interest you can be found here:

About the Author

Charluz M. Arocho Rosario

Originally from San Juan, Puerto Rico; Charluz completed her Bachelor's Degree in Animal Science at the University of Puerto Rico Mayagüez Campus. She obtained her Master's in Science in Veterinary Entomology from Texas A&M University where she is currently pursuing her PhD. 

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© 2019 by Women in Ag Science. 
 

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