Editor’s note: Conrad Berube, an entomologist and beekeeper (and senior IPM officer with the British Columbia Ministry of Environment), has spent more than 40 years working with highly defensive stinging wasps and bees, particularly tropic-zone evolved honeybees (so called “killer bees”), in North, Central and South America, Asia and Africa. Berube has been the triggerman for the 2019 extirpation of the first (and so far only) nest of Asian giant hornets (Vespa mandarinia) discovered in Canada1. Below is the full-length feature from Berube that is geared towards pest management professionals and it includes a description of the basic biology of social wasps; information on the identification of Asian giant hornets (AGHs) and their kin; personal protection recommendations; and tips for safe nest removal.
When I was putting together this article and a related presentation for the Canada Pest Management Association, gathering what we used to call audio visual materials, I was in an old vinyl records store and came across a sound-effects disc called “Buzzta rhyme: from the wasp nest”. I took it home and put it on the turntable and started listening… Something wasn’t quite right as the noises were similar-- but didn’t quite sound like wasps. Then I realized I was listening to the bee-side. Such confusion about properly identifying target insects will be a running theme throughout this attempt to provide a brief summary of everything that pest control professionals should know about the Asian Giant Hornet, Vespa mandarinia, known, now, more commonly as the "murder hornet." As you will read, there may be very little that you have to know about this critter—so, although I will be focusing on this species I will broaden, whenever possible, the topics I discuss to the wider subject of what you should know, generally, about dealing with stinging social wasps and bees.
I’ll use the framework of Integrated Pest Management to structure this article with the objectives that, by the end, you should be able to:
• Describe the basic biology of social wasps,
• Identify nests of Asian Giant Hornets and their kin,
• Protect yourself from stings-- and apply first aid if you don’t quite fully avoid getting nailed,
• Remove/eliminate nests of stinging wasps with minimal risk to yourself and clients.
First, though, as a bit of personal introduction, my surname may hint at my French-Canadian roots grafted on to a youth spent in Michigan, through which I hold dual American/Canadian citizenship-- relevant because my dual citizenship made me eligible to serve in the U.S. Peace Corps in the early 80’s. As a volunteer, and then as a technical trainer with the Peace Corps, and throughout the intervening years with other development projects, I have provided guidance in managing African-derived honey bees (the so-called killer bees) in Ecuador, Guatemala, Honduras, Paraguay, Tunisia, Nepal, Ghana, Guinea, and Uganda. In addition to these four decades working with highly defensive strains of Apis mellifera, a couple of decades back, I collected nests of all the species of stinging wasps in BC-- to provide venom to a pharmaceutical company for the purification of desensitization serum for the treatment of sting allergies. Because of this, I had all the equipment, and perhaps some acquired immunity that would be useful for contending against hornet venom, and I was able to serve as the triggerman for the 2019 extirpation of the first (and, so far, only) nest, discovered in Canada, of Asian Giant Hornets .
(Also, on the issue of names, entomologists usually separate descriptors of insects that are legitimately identified in the correct taxon by their common name: house fly, dung beetle, wax moth, etc. If a common name includes a reference to the wrong insect order, then the names are lumped together: butterfly, cutworm, ladybug, etc. Despite having to constantly battle with the autocorrect function of my word processor, I have gone with "honey bee" in this article, as opposed to what artificial intelligence assures me should be "honeybee.")
As further background, in August of 2019, Nanaimo beekeeper, John Duff, collected unfamiliar, very large wasps harassing bees at his backyard beehive. He sent specimens to BC Provincial Apiculturist, Paul van Westendorp, who confirmed these as the first specimens of the Asian Giant Hornet, Vespa mandarinia, found in North America. Notified of the find, John and Moufida Holubeshen, Nanaimo Beekeepers Club officers, near miraculously, discovered their nest during a dusk recce in a nearby park-- immediately after which they called me to take it out.
At the 2020 British Columbia Structural Pest Management Association conference, I explained how our bespoke band of beekeepers beat back the bee-eating beasties by besieging their burrowed bunker (using a lot of b’s there but saving a lot of bees in BC). I have posted a version of that presentation on Youtube (“Alien Giant Hornet Invasion” )-- and the Discovery channel’s streaming service hosts "Attack of the Murder Hornets" as CBC Gem’s platform does for "Invasion of the Murder Hornets" , each of which detail the Nanaimo discovery and extirpation. Therefore, I'll only be going into those details relevant to sharing tips for staying safe when working with poking pests-- and to mention that neither the extirpation, nor this article, are directly related to my role as a Senior Integrated Pest Management (IPM) officer with the BC Ministry of Environment and Climate Change Strategy—or, in standard disclaimer parlance: any views or opinions presented in this article are solely those of myself and do not necessarily represent those of the ministry.
To continue laying foundational groundwork, let’s review the principles of Integrated Pest Management which, with some variations depending on source, are, generally agreed to be Prevention and Planning, Identification and Information-gathering, Monitoring, Injury threshold-setting, Combined Controls, and Evaluation… which can be remembered with the mnemonic device “pi-mice”. Having said that, I’m going to start the story of the Asian Giant Hornet (AGH or Vespa mandarinia—monikers that I will be using more frequently than “murder hornets”) with the identification of specimens discovered in Nanaimo in late summer of 2019—rather than with prevention. (But starting with “Identification” would have resulted in the mnemonic for remembering the components of IPM being “i-P-mice” and I thought using that as a memory device would be somewhat off-putting.) Anyway, 2019 was an odd year for Asian exports to North America. While goods from China were restricted in a trade war, hornet detections near the Canadian/U.S. border were exceptional. In May of that year a live specimen of Asian hornet, Vespa soror, was collected in Vancouver's port area . Closely related to the AGH, this species is widely distributed in southeast Asia and has not been detected since. In contrast, in September, specimens of Vespa mandarinia were discovered in Nanaimo, BC, and, in December, in Blaine Washington-- and nests of the AGH were ultimately discovered in each locale.
Although all the specimens were superficially similar, very large, 1.5 to 2 inches long with large heads and striking orange and black markings, genetic analyses of the insects have indicated that the hornets found in Nanaimo were of a biotype typical of varieties found in Japan and distinct from that found in Washington aligned with hornets found in Korea . This is all to say that at least three different queens of two different species of Asian hornets were detected near the BC/WA border in 2019. Relating this back to pest control professionals, certainly, no one expects frontline technicians will be conducting mitochondrial DNA analyses to determine the identity of hornets about which they are called… but proper identification will link to a knowledge of life histories that will critically inform all aspects of IPM. And for pest control purposes, ID will be simple… you’ve got Asian Giant Hornets if you are in BC and observe black and orange wasps as large as your thumb emerging from their communal nest.
But many have been, and will be, reports of AGH-- which turn out to be often surprisingly unrelated insects. I received photographs from a concerned citizen which turned out to be a burying beetle that is only about twice as long as the sting of the AGH—which shared only an approximately similar colour scheme. There are useful posters available from BC and WA state public agencies to assist in distinguishing between AGH and supposed look-likes. A public graphical database of such reports, including confirmed identifications of AGH, is maintained by the Washington State Department of Agriculture (WSDA). (It is probably worth highlighting that the European hornet, Vespa crabro, is present in some parts of southern Ontario and Quebec and will likely cause concern whenever stories of Asian Giant Hornet hit the national press.)
Let’s take some time to consider the life cycles of honey bees and wasps to understand how those differ and how those differences influence population dynamics and IPM. I’ll start with honey bees because I suspect their biology might be more familiar to most readers-- and because it is largely the concern over the potential impact on the crucial role of honey bees as pollinators in the agricultural system that the AGH might make, in addition to risks the hornets may pose to public safety, that makes them of interest. Also, other social Hymenoptera and, in particular, honey bees are the principal prey species for the AGH and share many biological similarities, so many of the IPM strategies will be linked to apicultural practices. I’ll note here that there are many species of honey bees but I will make reference to only two, Apis cerana, which I will also sometimes refer to as the Eastern honey bee (because it is native to the Orient), and Apis mellifera, the Western honey bee native to Africa and Europe. In appearance and general lifestyle, the Eastern honey bee is a more diminutive cousin of the Western honey bee—but does have some distinctive behavioural differences. Honey bees reproduce through the fissioning of perennial colonies. If a honey bee colony is strong enough its queen will produce male (drones) and female (gynes or queens) reproductives. When the virgin gynes are about to emerge from their pupal cells the colony splits and the old honey bee queen will leave with about half the population of infertile workers to, hopefully, establish a new colony in a suitable nesting site. An emerging queen will inherit the old nests’ resources and will soon thereafter venture forth to mate with drones-- ideally from another colony. The drones’ role in the life cycle is basically to feed from the colonial stores-- to fuel forays for seeking out queens making their nuptial flights. During these orgiastic aerial acrobatics, the male’s genitals essentially explode, resulting in his shuffling off his mortal coitus. They feed, breed, and die during the deed, or as has been summarized more succinctly by others: honey, nut, cheerio.
In contrast to honey bees, whose colonies may persist for long numbers of years, eusocial wasp nests, such as those of hornets and yellowjackets, are annual affairs. An overwintered mated queen wasp will seek a suitable nest site in the spring, construct the first set of cells, and begin rearing worker brood. The resulting infertile female workers will take over foraging and comb construction, from their mother, so that she can concentrate on laying eggs. Like all insects with complete metamorphosis, the eggs hatch into larvae that then develop into pupae and thereafter adults. Combs in the nest are constructed of a sturdy cardboard-like material that the workers make from wood scrapings that they collect, chew into a pulp, and then form into the hexagonal cells characteristically used by social wasps and bees. The brood in these carton creches is assiduously attended by the workers. During the growing season workers are diligent caregivers and the ferocious temperament of the Asian Giant Hornet is inherently linked with their intense devotion to caring for their immature sisters. But their dedication is not entirely altruistic. Adult wasps are apex predators at the top of the food chain, but the adults cannot digest the flesh of the insects they collect—as solid foods cannot pass through their wasp waists. Instead, the workers mash up the prey and feed the resulting hornet-made hamburger to their larvae. The larvae scrape the sides of their cells to create a signal that serves the same purpose as the cheeping of baby birds—it is a constant call for food. The larvae digest the insect meat pellets brought to them and then regurgitate a slurry rich in amino acids and other nutrients? on which the adults subsist — so adults and workers are mutually dependent on each other for food, ensuring colonial cohesion . (The technical term for such communal food sharing is “trophalaxis” and is important in the control of other insects-- such as ants and cockroaches-- through the use of poisoned baits that are passed around to spread throughout the so-called social stomach.)
Much in the way that honey bee royal jelly is ascribed magical human nutritive powers, in Asia, this larval regurgitant is glamourized as an athletic performance enhancer and is produced synthetically as “VAAM” (Vespa Amino Acid Mixture). I suppose, if life deals you lemons, you might as well mix the pest with it. In Japan, this synthetic hornet vomit is included as an ingredient in a booster tonic that is touted as improving endurance during sporting activities, apparently by inducing ketosis . Asian Giant Hornets themselves have found their way into the human diet and are considered a delicacy in some areas—although I wonder if cunning beekeepers might be perpetuating the idea to promote wasp consumption, so it keeps AGH populations down. The adult wasps are also drowned and steeped in an alcoholic beverage, shochu, as the venom is believed to imbue the liquor with additional pleasant intoxicating properties . That venom is normally delivered, defensively, through ¼ inch stings deployed when the hornets are threatened. I’ll return to why these human dietary choices might be relevant… but let’s get back to AGH dietary concerns.
As the season progresses, larval population demands increase and the hawking behaviour on individual bees may change to concentrated assaults on an entire colony . AGH prepare for this slaughter phase by marking hives with a pheromone that assists their nestmates to locate and target their prospective victims. As their native ranges overlap with that of the AGH, Eastern honey bee colonies that survived to reproduce were those with effective defense strategies. We can emulate some of the tactics that the Eastern honey bees evolved. The bees collect plant resins and animal feces that they smear around their nest entrances in response to the marking with the AGH pheromone, which appears to mask the AGH odor post-it . In addition, when they detect AGH, eastern honey bees hastily retreat into their hive and hunker down. If a hornet enters their hive and attacks, the bees will scrum on top of the intruder. Apis cerana is more tolerant of the heat and carbon dioxide concentrated within the bee ball-- which overwhelms and kills the marauding hornet .
Western honey bees, in contrast, evolved outside the range of the AGH and have defensive strategies that are not as effective against them. Colonies of Apis mellifera introduced to AGH territories, when targeted by them, will fly out to meet them in aerial dogfights. But the bees are grossly outmatched in such conflicts and a few dozen AGH can decapitate the entire adult population of more than 30,000 bees within a few hours. They then occupy the conquered hive, abandoning the bodies of the adult bees to concentrate on ferrying the soft bee brood back to feed to their own larval sisters, fueled by the rich honey stores of their victims . Provisioned in this way, the AGH nest can grow to about soccer ball-sized volumes. These nests, in their native range, are almost always found underground, as was the Nanaimo nest. Strikingly, however, all four of the nests found and destroyed in Washington have been found aboveground in tree hollows-- three of them several meters aboveground . AGH are not capable of making exposed nests like those of some yellowjackets (which include the bald-faced hornet—which is technically, an off-color yellowjacket and not a true hornet). In the fall, male and female reproductives are produced with mating taking place near the nest entrances from which the females emerge . The mated females seek appropriate shelter in which to spend the winter months, in the case of the AGH these may be abandoned rodent dens or similar cavities in the forest floor, or they may excavate their own so-called hibernacula in the loamy soil or forest duff. In the spring the cycle repeats.
Let’s review some of the life history identified-- which will be important in IPM:
• AGH are thumb-sized black and orange imported wasps sharing a soccer-ball sized nest constructed within a cavity (normally underground in their native range but, so far, in the Pacific Northwest, more frequently found in tree hollows).
• The AGH defend themselves with potent ¼ inch long stings that can penetrate several layers of clothing.
• As they are obligatorily colonial, the hornets share a social stomach as food is transferred amongst members of the nest.
• AGH are apex predators specializing in social insects, including, and especially of concern, honey bees, for which they search, throughout the summer and, especially, in the fall.
Ok, that was an awful lot of groundwork to lay— and the bulk of what I’ll have to say—but it will serve as our base from which hornets we’ll slay (sorry, I didn’t intend to do that-- but I got halfway through the sentence and couldn’t help myself)… but let’s now go back to the prevention and preparation step of IPM to see how the foregoing was relevant.
As they are native to Asia, routine border protections are the first line of defense in preventing introductions of AGH-- and any other potential pest species. The Canadian Food Inspection Agency has treatment and inspection programs that reduce the chance of pests crossing borders as stowaways in freight. Remember my mentioning the several gastronomic uses to which AGH are put. Live AGH larvae have been seized at border crossings, presumably from folks wishing to use them in food or drink preparations . Such precautions are not always effective and researchers in France traced the introduction, there, of another Asian hornet, Vespa velutina, the yellow-legged hornet, to a shipment of flowerpots from China . Stacks of earthenware pots contain gaps that hornet queens could enter through the drainage holes—resembling, as they do, preferred overwintering sites. Springtime loads of terracotta flowerpots, bound from Asia for the nursery industry, could contain stowaway AGH queens. Apparently, something similar occurred to allow AGH queens to establish nests near the BC/WA border in the past several years.
On September 19, 2019, following up on nearby specimen catches by a fellow Nanaimo bee club member the month before, beekeepers John and Mofida Holubeshen, made the sunset discovery of the first Asian Giant Hornet nest in North America. Along with bee club president Peter Lange and myself, we mustered onsite and began preparing ourselves for the coming confrontation. Reducing stings was at the forefront of our minds, since we had read about the necrotic tissue damage that can result from the stings of AGH. The venom of Asian Giant Hornets is likely no more potent than that of other stinging Hymenoptera, but, because of their large size, they can deliver a greater dose in any single sting—an AGH worker holding about 4.1μl of venom , about 8 times that of a honey bee.
The key to reducing sting incidents is by managing the components of what I have come to think of as the sting triangle (analogous to the fire triangle for combustion). If you can reduce or eliminate any component of the triangle you can lessen the risk of stings. If you eliminate the bee or wasp population, no risk of stings. If you can prevent disturbance to the wasps or bees, no risk of stings. If you can prevent yourself from being a target, no risk of stings.
Our goal was to eliminate the hornets-- by which we were necessarily going to cause a catastrophic disturbance to the colony. So the component for which we could exert the greatest amount of control was in protecting ourselves as targets. In this, we used many techniques that echo those that honey bees employ.
Much like the Eastern honey bees that speed return flights when encountering AGH, the simplest tactic to avoid stings is to beat a hasty retreat. Should you be caught without gear and disturb a wasp nest, shield your eyes with your fingers, to protect your vision, and beat it out of there as quickly as possible. On flat level ground, most of any pursuing workers will give up the chase within a few tens of meters . If there is such, you can dodge through leafy vegetation to conceal your retreat and to brush away any persistent pursuers.
With the luxury of prep time, we can employ other techniques that are utilized by honey bees—such as the element of disguise… Recall that I noted that Eastern honey bees smear foraged feces at their hive entrances that masks hornet pheromones. This is an important tactic that should be imitated when working around stinging Hymenoptera—but it need not involve dousing oneself with do-do. (Although, by an odd coincidence, while preparing this presentation I heard a podcast in which it was mentioned that, during World War II, the Irish parliament building was daubed with dung, and coal dust, to camouflage its distinctive stonework from air raids—and it has never been successfully restored to its original colour .)
Beekeepers routinely use smoke to mask the smell of alarm pheromone at a sting site and, so you don’t need to bother with a bee-bellows, slathering on some liquid smoke over the face and head can similarly reduce the chance of being stung-- if a wasp is able to work its way under one’s veil. Wasps and bees “taste” with their feet and essentially, the smoke flavoring will act as a repellant when the stinging insect is attempting to position itself on your skin to sting… giving you enough time to step away from the nest, mash the insect inside your veil and to remove it before returning to the nest area. (As an aside, beekeepers also puff a little smoke into hives before working them, because it causes the workers to busy themselves with eating honey which will fuel their escape if the nest needs to be abandoned. Bloated with honey, the bees are more reluctant to rise from their combs and are slower to sting.) The honey bee sting mechanism is barbed-- and a bee disembowels itself and dies soon after leaving its syringe-like venom sac behind. If stung by a bee, you can at least take some solace that the bee got the worst of the bargain. Nonetheless, the disembodied venom sac will continue to pump toxins into the skin-- if not immediately flicked off with a thumbnail or such.
In contrast, wasp sting lancets are smooth-- and a single worker can sting repeatedly.
The sting organs of Hymenoptera are modified from the organs that, in other insect species, such as parasitic wasps, form ovipositors. So the male bees and wasps, the drones, cannot sting. Most of the individuals in a colony are, however, fully-armed female workers, so it’s good practice to lay in a supply of first aid when tackling nest removal. Those who are severely allergic to wasp or bee stings often carry an Epi-pen to prevent anaphylactic shock… but these devices would be overkill for the normal pain and swelling that one would expect from being stung. I received at least seven stings in the course of removing the nest. The first four were the worst of those stings, and felt like red hot thumbtacks being driven into the flesh. Two of the first/worst stings drew blood and the resulting scars were still evident a year later.
Within a few hours of receipt, I took a couple of Ibuprofen for the persistent pain from the four stings I’d sustained across the thighs-- but I didn’t bother with an antihistamine to reduce swelling (to which I am not much prone, given my long history of exposure). However, pest control professionals may want to lay in a supply of these-- if they are going to be taking out any kind of wasp nest. I didn’t swell very much, but for the next twenty-four hours or so, I had throbbing in my legs similar to the muscular ache one often gets with flu.
Getting back to our preparations for the nest assault-- in addition to a hickory flavoured face wash, we bolstered our normal beekeeping gear, veiled bee suits, and long-sleeved, heavy gloves, with extra-thick clothing. As I had volunteered to conduct the actual nest extraction with Peter, John, and Mofida acting as support crew (and potential medevac team), I was also sporting Kevlar bracers at wrist and ankle and a bulletproof vest of the kind normally used for chainsaw safety or in zombie apocalypses. In hindsight, that was a bit of overdressing.
Night had already fallen, making it the ideal time for dispatching a wasp nest. Social Hymenoptera largely return to their nests at day’s end (although occasional stragglers may get caught by the dark, in which they cannot fly, and then overnight outdoors)—so the great majority of the colony is in the nest at nightfall. It is in such conditions that wasps who build aerial nests can be collected with their entire population by simple bagging—with minimal risk to the collector or bystanders. The collection of enclosed or subterranean nests is a bit more complicated but, likewise, is ideally performed at night. Even at night, appropriate personal protective equipment (PPE) should be used along with other gear necessary for nest removal.
Now, keep in mind that I said wasps and bees don’t fly in the dark; if you are using lights to see what you are doing while you collect such insects it’s no longer dark. Wasps and bees will fly toward headlamps worn by nest raiders, so, it’s recommended that you set up a light source detached from your person to illuminate your work-- using your headlamp intermittently as necessary. Once properly girded, comparisons are naturally drawn between wasp-hunters and ghostbusters, either because of similar Canadian fashion choices or because the high-end protective garb favoured by WSDA collectors makes them resemble the Stay-Puft Marshmallow Man.
There’s a huge difference in price ranges on anti-sting wear. I wear a low-cost bug jacket that is cool in the hot weather, in which I often work, and which can easily be bolstered with extra layers of clothing. Frankly, I think the high-end suits favoured by the WSDA, if used by less diligent personnel, might promote a cavalier attitude that could result in cutting corners on safety protocols, such as removing nests near dwellings during daylight hours—which could expose unprotected bystanders to sting risks if used for routine wasp removals—or if AGH eradication becomes a more commonplace necessity.
Whatever outerwear choices are made, it’s a good idea to wash or rinse down protective gear if any significant amount of alarm pheromone has been deposited on it during sting incidents.
In addition to PPE, the following are recommended: flashlights and headlamps, collection bottles and containers, garbage bags, isopropyl alcohol, a carbon dioxide fire extinguisher, a vacuum cleaner, aerosol wasp and hornet killer, a shovel, a small saw, and large knives, and a tote to carry all the kit. But I will talk about most of that when I discuss control options.
To recap key points of Prevention and Planning:
• Government agencies are conducting efforts to prevent AGH from establishing itself in North America.
• Once located, nests of AGH, or other wasps or hornets, are best dispatched at night.
• First aid equipment should be kept ready to hand in case strategies to avoid stings are ineffective
• Proper personal protective gear and a variety of special equipment are necessary to safely remove nests.
So, we’ve covered Prevention and Planning, and Identification, which brings us to Monitoring. As is usually the case in the structural industry, it is very likely that initial monitoring to detect the presence of pest wasps, including the AGH, is going to be conducted by your clients. For run-of-the-mill wasps, clients will likely contact you only after they have visually located a nest on their property. But you may occasionally be contacted by someone who believes they have trapped an AGH and wants you to do something. There is no legal requirement to report AGH but you are certainly encouraged to do so. At least that's the case for most people… beekeepers, in BC, are required to report novel diseases impacting their bees (which, oddly, includes insects under the legal definitions) under the provincial Bee Act . In BC, reports can be made with a photo attachment of the suspected AGH, via email, to email@example.com but you can also use the WSDA reporting venues including firstname.lastname@example.org or email@example.com. The Canadian Food Inspection Agency monitors for a variety of potential pest species. After the Vespa soror specimen had turned up near Vancouver’s port, the CFIA had deployed some commercial wasp traps to monitor for additional hornets. It was only after our Nanaimo extirpation that I advised their reps that those traps had apertures too small to allow entry of the wasps for which they were intended. The commercial traps had to be altered by boring larger entries to serve in monitoring for Asian hornets—but much more economical alternatives can be made by recycling 2 litre soft drink bottles.
The design is simple enough that you’d likely be able to come up with a workable unit just from seeing an example-- but detailed instructions can be found on a WSDA site --and, as mentioned, citizens living near the BC/WA border are encouraged to participate in trapping programs and to report catches or incidental sightings of AGH. A graphical database of such reports, including confirmed identifications of AGH, is maintained by the WSDA .
Many beekeepers are participating in AGH monitoring programs. Some already routinely use devices intended to prevent wasps from preying on hives-- as established yellowjacket species cause significant bee losses. Sticky traps are the preferred method of dealing with Asian Giant Hornets harrying Western honey bee colonies in the native range of the hornets and likewise, in temperate zones, are more effective than bottle traps -- if the AGH nest cannot be located. For yellowjackets, a water bath trap baited with meat or fish will not attract bees and seems to be more effective than bottle traps .
But any such trapping is only good enough to indicate that a nest may be active in the area. More laborious methods are required for locating nests and, frankly, those are probably best left to parties working with government to prevent the establishment of AGH—as the exercises are likely to be time-consuming or otherwise prohibitively expensive. The Washington State Department of Agriculture has used radio tags, small enough to tie to live-trapped hornets, to track them back to their nests and has been experimenting with infrared spotting technology. As a traditional alternative, streamers can be attached to balls of fish left out as bait for hornets to carry back home or to the hornets themselves to assist in visually following released hornets to their nest .
Key points on monitoring:
• Most trapping is conducted by citizen scientists, especially beekeepers, and any suspected AGH caught in traps, or incidentally spotted, should be reported.
• WSDA has used radio-tagged hornets to locate four nests so far.
• It’s likely not worth attending to a complaint of AGH, or other wasps, unless a prospective client reports a nest location.
This brings us to Injury Thresholds: As is the case for most structural pests, the injury threshold at which control measures are justified is based on client tolerance to a pest’s presence-- and confirmation of the actual presence of that pest. (That qualifier being necessary because of the not uncommon dynamic of “paper mites” -- or even delusory parasitosis -- in which clients misidentify-- or imagine-- pests being responsible for unquestioningly real symptoms that are, in reality, attributable to causes other than pests.) On a related note, don’t forget that, in BC, if control measures include a non-Excluded pesticide, as defined under the province’s Integrated Pest Management Regulation, then pesticide use records must include the associated monitoring and injury thresholds. So, in the case of AGH, such documentation could include: “Presence of Asian Giant Hornets, beyond client tolerance, was confirmed by collection and i.d. of specimens and visual observation of an active nest.” That’s it. Simple. (Keep that format in mind when documenting treatments for other pests.)
• Locating an active nest of stinging insects posing a risk to public safety is a valid injury threshold.
• Don’t neglect to document observations in pesticide use records.
Now we’re ready for Control options. Physical control options for stinging insects can be amongst the easiest jobs that pest control professionals provide—or amongst the most challenging and hazardous to both technicians and their clients. As I emphasized earlier, if you can schedule control options until after dark you will be maximizing your impact and minimizing liabilities. Aerial nests of several species of wasps and hornets can easily be bagged after dark with heavy-gauge plastic or pillowcases (don’t use anything too flimsy that the insects can easily chew through). Once bagged, put your catch into a cooler with plenty of ice and transfer the bag into a low-temperature freezer at the earliest opportunity, leaving them until the insects are completely frozen for several hours.
So far, the nests discovered in WA have been in tree hollows amenable to similar collection. The bole of each tree was wrapped in heavy cellophane to seal the entrance, the extent of the hollow determined by thermal imaging or sounding, and then the trunk was cut, through sound wood, above and below the nest. Then the whole tree segment was transported to a large freezer unit and the nest cooled to lethal low temperatures.
Portable vacuum units can be used to mop up any workers that escape bagging operations. I have often used a vacuum cleaner, with a collection bottle spliced into the suction hose, to collect wasps—but there was no electricity available near our Nanaimo nest site and the small handheld, Dustbuster-style unit that I’d brought proved to have too small an opening to allow the entry of AGH workers. In fact, it was while attempting to vacuum some specimen hornets, when initially approaching the nest, that I took my first four stings—across my upper thighs where the fabric had stretched tight as I squatted next to the nest.
Keeping in mind that the nozzle must be ample enough to allow entry, a vacuum can still be a useful tool to collect workers returning to the nest, particularly if circumstances require that nest removal occurs during daylight hours. DIY collection bottles are easily made and incorporated into vacuum devices. The chamber can be dosed with carbon dioxide to anesthetize hornets before transferring them into another container and thence into the cooler.
CO2 can also be applied directly to the nest if specimens are to be collected for research or commercial purposes that would preclude the use of pesticides (such as for venom extraction, genetic analyses, or sale of prepared exhibits). The insects can be preserved in isopropyl alcohol, onsite, as an alternative to freezing. Keep in mind that, while you can put the insects into alcohol, you can’t legally spray the alcohol into the nest-- as it is not registered as a pesticide.
Drowning the hornets with water is not advisable as you’d not likely be able to overwhelm the nest in that manner before many of its inhabitants had emerged to reek their rage upon you. But, attempting that would not violate Canadian pesticide regulations-- since that would be a physical control measure (much like hermetically sealing off the nest). I've argued that blowing CO2 into the nest to kill the hornets would, similarly, be a physical control measure—as the CO2, per se, is not toxic to the insects but, rather, is just displacing oxygenated air and asphyxiating them (i.e. is “drowning” them with gas rather than liquid). However, I checked with the PMRA and they don't agree… i.e. if you want to kill hornets, rather than anesthetizing and collecting them for disposal by other means, don't use CO2. And, in any case, there are plenty of aerosol wasp and hornet pesticides that are registered —many of which include foaming agents that inhibit the hornets from leaving the nest—but which, therefore, may not permeate the brood combs sufficiently to ensure complete control. In addition, I would not want to depend solely on those products to knock the insects down quickly enough to prevent their defensive response without using the other protective and control techniques mentioned. Do not exceed doses specified by labels and do ensure that you heed any time-related precautions related to efficacy and re-entry or with handling the nest.
While on the subject of what not to do, it has occurred to more than one person to poorly emulate the Eastern honey bees’ heat treatment technique for killing hornets—by using fire. There are several “Fail Army” or “Darwin Award” style stories on the internet demonstrating why this is not a good idea, many ending in injury or other damage -- or arrest. Fire is not a recommended control tool for wasps.
There are no insecticidal baits registered for use against wasps and hornets in Canada (as there are for ants and cockroaches-- for which bait stations are used indoors and/or are designed to restrict access to non-targets). Such baits for wasps could represent a risk to bees and other non-targets-- so locating the nest is the only means of properly destroying a colony. On a similar theme, there are very few pesticides registered for use against bees. Although it is not illegal to kill honey bees that represent a hazard, in the increasingly rare circumstances that they establish themselves near a household, the removal of a honey bee colony is best turned over to a local beekeeper, who will transfer the colony into a hive and remove it to their apiary. But if you simply spray the colony, and leave the combs behind, these can attract other insect and rodent pests to the nest site and the honey may cause physical damage to structures if the comb melts/breaks and leaks, once unattended by bees.
I’m not sure if the following would be considered wasp controls or, rather, prevention but it really only matters if you are a beekeeper-- and some of these probably won’t matter even then--but I just found them kind of interesting: Bee houses are already commonly used in many parts of the world and can be retrofitted with screens to filter out hornets; similar screening and entrance reducers could be employed on individual hive entrances.
Sarracenia purpurea L., Northern Pitcher Plant, native to North America, was tested-- and found wanting-- as a naturally-reproducing biocontrol agent against hornets in Europe . I have found evidence of bee moths, Aphomia sociella, several times in yellowjacket nests in BC and WA—and similar species have been recorded in nests of Vespa mandarinia in their native range —but, in neither case do they likely represent a significant mortality factor. Very rarely, colonies of AGH have been recorded as having been destroyed because of early parasitism by Strepsipterans or stylops . And I just mention them because they are so weird. Female stylops parasites spend their adult lives protruding from the sclerites of their Hymenopteran hosts . The males are free-living and capable of flight once they have emerged from the bee or wasp inside of which they have passed their larval and pupal phases. Imagine the indignity of having a parasitic pigeon’s hindquarters sticking out of your belly button and its horny husband flying by occasionally to mate so that your hitchhiker could drop fertilized eggs whenever you were at your favourite feeding sites.
Aside from these novel natural enemies, whatever technique you use to dispatch wasps, you should dig up or cut out the nest, as appropriate, to ensure that control has been effective in all parts of the colony.
To review, Control options include:
• Physically containing the nest in a bag or such and then freezing it.
• Vacuuming wasps as they emerge from the nest and/or as combs are slowly exposed.
• Physically stunning the wasps with CO2 and then preserving them.
• Using registered aerosol pesticides
By whatever means wasps are disposed of, the nest should be dug up or cut out and removed…which brings us to Evaluation.
Much like Injury Threshold, Evaluation for wasp nest control is quite simple: when you confirm the nest has been effectively dispatched, your evaluation may be considered complete.
Once a nest is destroyed, any remaining workers will not re-establish a colony (and nests depopulated in the fall, as colonies die off, are not reused the following season). Nonetheless, it is worth encouraging clients to continue to trap for AGH or yellowjackets, especially around beehives as there may be other nests in the area.
What might be the impact if AGH became firmly established in North America? Most wasps, in the broad sense, represent no threat to bees as they are specialized parasitoids. However, when most people think of wasps they're thinking of yellowjackets—and most of our yellowjacket species are predatory on honey bees. Since AGH are bigger and clumsier than other wasp species and are not great at tackling fast-moving species like solitary bees (which characterizes, by far, the bulk of our native bees) the imported Goliaths likely would not have a significant impact on solitary bees. The AGH specialize in attacking other social wasps and honey bees by hanging out at their nest entrances and picking them off when they land or by invading their nests. So far, there is only one report of a honey bee colony kill, in Custer, WA, that is likely attributable to AGH and it is unclear how the establishment of Vespa mandarinia in North America would affect beekeeping economically-- but the cumulative European cost of just the control programs for a related species, Vespa velutina, since its 2004 introduction to France, has been about US$30 million... not counting the costs of lost honey and pollination services-- and related agricultural production . Monitoring methods include simple passive trapping and more high-tech approaches such as, again, radio tracking and thermal imaging, followed by physical destruction of nests. If AGH spread into all ecosystems in the U.S. and Canada to which it was suited, it could threaten income of US$11.9 million and $101.8 million for hive-derived products and bee-pollinated crops production, respectively .
Since we destroyed the Nanaimo AGH nest in September 2019 (at a cost of about US$100 to replace my fire extinguisher-- which was past its legal refill date), no nests in BC, or elsewhere in Canada, have been detected. In November 2019, an AGH worker was found in White Rock, BC, and in 2020 four workers were collected in the province (two in Langley and one each in Bradner and Aldergrove) . In Surrey, BC, one worker was collected in 2021, about 22 meters from the U.S. border, and very soon after a nearby nest had been destroyed in WA . So, there certainly does not seem to be any looming threat—so long as eradication efforts in WA prove successful. However, the management tactics I have discussed can easily be used with other stinging Hymenoptera.
To recap, the key tips I've recommended, beyond those that most pest control professionals routinely employ are:
• eliminate wasps at night, if possible,
• use smoke odour on the skin as a repellant,
• gird oneself with appropriate PPE.
Of course, the general IPM strategies are applicable to all pests. Let's all hope that things continue as they have for the past few years so that it will never be necessary to use the somewhat symmetrical wasp-spawned gasp of "Agh! It's an AGH!"
1 Health Canada. Consumer Product Safety, Search Product Label tool
2 Serna, J. (2019) "He feared being stung by wasps and accidentally started California’s biggest fire." Los Angeles Times, Posted: Jun 8, 2019.
3 Wycke, M. A., Perrocheau, R., and Darrouzet, E. (2018). Sarracenia carnivorous plants cannot serve as efficient biological control of the invasive hornet Vespa velutina nigrithorax in Europe. Rethinking Ecology, 3, 41-50.
4 Matsuura, M. (1984). Comparative biology of the five Japanese species of the genus Vespa (Hymenoptera, Vespidae). Mie University, Departmental Bulletin Paper.
5 Matsuura, M. ibid.
Beani, L., Dallai, R., Mercati, D., Cappa, F., Giusti, F., and Manfredini, F. (2011). When a parasite breaks all the rules of a colony: morphology and fate of wasps infected by a strepsipteran endoparasite. Animal Behaviour, 82(6), 1305-1312.