Asian Giant Hornets Not a Problem for NC Beekeepers…yet?

— Written By

There is a viral news story circulating about the “murder hornet,” the unfortunate moniker of the Asian Giant hornet, Vespa mandarinia. To the entomology world, this news is actually a bit old, as it was first reported in December 2019, where a small handful of colonies were reported in the Pacific Northwest (and nowhere else in North America). As such, there are no documented cases of this new invasive insect in North Carolina.

Many folks have been mistakenly confusing the European hornet, Vespa crabro, as this newcomer, as to the untrained eye they look very similar. Rest assured, though, these are a different species that we’ve had in NC for quite a while, and they pose no significant threat to beekeepers (although they can, like many social stinging insects, pose a minor risk to public health).

The “murder hornet” nickname was coined not because of it rarely kills people but instead they can prey on honey bee colonies. Like all wasps (which are predatory), they collect sources of meat for their protein (unlike bees, which collect pollen from flowers, and are thus vegans rather than omnivores). Since honey bee colonies are a convenient concentration of insects, these wasps can target beehives while foraging. Such attacks typically start in mid-summer, when the hornet populations are increasing, by first snatching a few adult workers from the front entrance. Later in the summer, when the hornet colonies are at their peak, they can become more bold; they can decapitate most if not all of the adult workers in a colony then steal all of the larvae, leading to the obvious demise of the honey bees often within only a few hours. As such, they should really be called the “Apicidal hornets!” rather than murder hornets.

Interestingly, in its native range, the Japanese subspecies of honey bee (Apis cerana japonica) has evolved an interesting nest defense against these predators. At the entrance, when an Asian Giant hornet tries to enter, some of the guard bees will pounce on the intruder and “ball” them, preventing their movement. The bees then exercise their wing motor muscles to generate heat (just like they do during winter), and in doing so they heat the wasp up to a lethal temperature, killing it. Unfortunately, this behavior has not been reported in the Western honey bee, Apis mellifera.

Robbing screen

Robbing screen on a beehive.

Regardless, beekeepers can significantly deter and prevent such predation by using robbing screens. While primarily used to deter other honey bees from stealing honey, they are also very effective for hornets and other unwanted guests. The majority of the entrance is screened over with #8 wire mesh so that only a small gap is open and is therefore much more easily defended. The entire entrance still emits hive odors, however, so unsuspecting predators continue in vain to get in passed the guard bees. Without using such preventative measures, thousands of A. mellifera hives can be affected each year in Japan.

Seeing that they’re not in NC, the issue for beekeepers in the state is moot, but it is something to be on our radar in the future. Hopefully, that is several years or decades away. Even when they get to North Carolina, their impact will likely pale in comparison to most of the more immediate problems with which beekeepers are already facing.