Yellow-Legged Hornets Have Arrived: What Beekeepers Need to Know
A.F. asks: I saw something online about Yellow-Legged hornets being established on the East Coast. Can you explain what’s going on and what it means for our hives in Kentucky?
Jake: Sure! The bad news first: despite earlier reports suggesting Yellow-Legged hornets had been eradicated in the United States, signs indicate the species has now established itself in Coastal South Carolina and Georgia.
This hornet is a bee predator, and will cause major challenges in domestic beekeeping as it spreads and radiates out from that established cluster. The Yellow-Legged Hornet’s diet appears to be 70% honey bees in urban areas and 30% in rural areas.
Identification
The Yellow-Legged hornet is pretty identifiable. It is a large dark hornet, black and yellow. It lacks the bright reds of the European hornet that’s been in the U.S. since the 1840s. The Yellow-Legged’s abdominal banding is also much simpler, lacking the teardrops or crenelations of the European. Unfortunately, the Yellow-Legged is similar enough to several other flying-yellow-stingy-things, so reporting programs will be plagued with false positives, much like the “murder hornet” call barrages hitting apiarist offices over the past few years.
Nest Cycle and Destruction
While it is established and is spreading, we have some opportunity to stall its spread by destroying nests where they are discovered. It has an annual nest and brood cycle similar to bald-faced hornets. A founding queen builds up a population of workers before finally producing reproductives that then winter individually, with the nest dying. Destroying a colony before the final reproductive hatch can greatly stall spread.
Interestingly, the Yellow-Legged does this through a series of nests! It produces three nests in a row, growing in complexity and size (images on next page). The initial nest, the embryo nest, is about the size of a coffee mug. The next stage is the primary nest, which can either be the embryo nest expanded or at a new site. The final stage is the secondary nest, which is generally high (60′) and massive.
The current modus operandi is when a nest is discovered, it is physically accessed and sprayed or gassed, to kill the entire population. The nest can then be physically removed. This prevents the escape of the reproductives during the abatement process.
One prominent feature of the nests are their pronounced swirl-patterned exteriors. They have the familiar internal plate structure seen in other large paper-nest building species. The primary nests can be basketball-sized, while secondary nests are quite large with over 5,000 inhabitants. As the population increases over the season, they become more discoverable.
What to Expect — and What to Do
The hornet has a unique “hawking” behavior where it stalks worker bees near a colony entrance, which means their presence will be readily noted by beekeepers in the late summer. (Initial detections in both GA and SC were by beekeepers.)
One short lived relief: in other regions where the Yellow-Legged hornet has been imported, its spread was about 50 miles/year. That means that Georgia and South Carolina will have significant experience with the hornet before it arrives in our apiaries. If you believe you have discovered Yellow-Legged hornets in your area, contact your state or provincial apiarist.
A Note on Naming: “Asian Hornet” Confusion
You might have noted special care in avoiding the phrase “Asian” hornet in the above article. That name has been applied to both Yellow-Legged hornet (Vespa velutina) in Europe and to the Giant Asian hornet (Vespa mandarinia, now called the Northern Giant hornet), another invasive also recently discovered in North America. Reports on “Asian hornet” control can be conflicting, often because they are discussing different species and invasions.
While Yellow-Legged eradication in North America seems no longer possible in the absence of federal intervention, programs for Northern Giant hornet control appear to have been successful in the Pacific Northwest. This is not to discount the efforts at the state level in both instances. Large commitments of time and resources at the state level occurred, and both continue with monitoring programs.
The Economic Case for Federal Action
In Europe, the arrival of the Yellow-Legged hornet induced colony losses of 30%. It also feeds on native pollinator populations, and has rattle-on impacts to domestic honey production and pollination. The hornets also feed on soft fruits like grapes, pears and apples. The U.S. climate is more ideal for the Yellow-Legged hornet as well, so we can expect worse outcomes than Europe has seen thus far.
To try and develop a damages-as-dollars figure, we can spitball impacts on pollination, assuming the hornet established and became endemic. Pollination revenue is about $400M/year, a loss of 30% of colonies could easily see that figure shoot up, maybe an additional $200M/year (recall the spikes in pollination contract values during CCD episodes). On that basis alone, we’re talking a $2B impact that would be passed to consumers over 10 years.
Effective federal intervention now could eliminate this threat at great savings to taxpayers. France’s large federal nest elimination program costs roughly $2.3M/year. An effective federal response in this limited area could be had for well under $20M, and with $2B in long term consumer savings, represents a 100x return in investment, before assessing the other savings.