The coming swarm
Every summer, a plague of wasps gathers, ruining picnics, harassing trampers and disrupting ecosystems. Wasps outcompete bees for food, costing New Zealand about $130 million each year in loss of honey and pasture crops. Where wasps abound, biodiversity suffers: butterflies disappear, songbirds stop breeding and invertebrate communities are looted. But there’s hope on the horizon. Scientists are developing weapons, both biological and genetic, in a bid to cure the pestilence, once and for all.
At last, these rays of September sun emit some faint thrum of warmth. Up here at St Arnaud, the forest has been in winter lockdown, but now it responds to the touch of the sun. Beech buds, clenched tight against the cold, unfurl. Tentative chirps of bellbird song ring off Lake Rotoiti. And beneath the parting bark of a fallen beech log, a queen common wasp stirs.
This tiny crawl space has saved her life. Wasps, like most insects, cannot generate any heat of their own, so she spent the winter at the mercy of the mercury: she cannot avoid freezing. Had she chosen a damper site, the rapid expansion of freezing water molecules within her body would have killed her, but here, wrapped in the waxy dry of cambium, special proteins and compounds have pre-empted freezing by building ice crystals inside her tissues, allowing her body to succumb in a measured, benign way.
The queen has huddled for months, her antennae curled, wings carefully folded beneath her middle legs. Back in May, she bit hard into the beech to anchor herself, then lapsed into torpor. Her metabolism has been barely ticking over since, taking tiny sips of energy from whatever fat she put aside for her long sleep. Now, some subtle threshold of temperature or daylight length has been crossed, and somehow, she perceives. In a primal reach of her brain, neurons begin to flicker.
She has survived the long dark of winter, but she must rouse herself quickly—spiders know just where to look for quiescent prey.
It’s up to her to rebuild her species. In New Zealand, more than 90 per cent of all common wasps die every autumn—only queens survive, and this one might fly 40 kilometres now, seeking the perfect nest site. It will probably be underground; perhaps beneath the upturned root ball of a fallen tree, or in a sunny bank.
If she chooses poorly, her lair will flood. A wet spring is the ruination of thousands of nests. She toils alone, chewing on soft wood, rasping fibres to mix with her own saliva to make a kind of papier mâché. With her mandibles, she fashions the first few cells of a new nest, then lays an egg—fertilised by sperm she has sequestered all winter—in each. Right now, the greatest danger comes from her own kind. Other queens are prowling—opportunists that will kill her and seize her nest if they can.
After a week, her brood hatches, and she roams the forest for protein and sugary offerings for them. When a fortnight has passed, the larvae spin their own silken prisons, and transmogrify. Cells migrate around their bodies, old tissues are subsumed and new ones formed, until, after another fortnight or so, an adult worker emerges. As the labour force grows, the queen dedicates herself solely to laying more eggs. From here, things go exponential. By March, she may have 10,000 subjects.
Her forebears—hibernating queens like herself—arrived in New Zealand in the late 1970s from Europe or Asia. They went unnoticed for years, because they look very similar to German wasps, which had been in the country since 1945.
It took a sharp eye to spot the incursion. During a break at a Dunedin science congress in 1983, entomologist Barry Donovan was waiting to cross George Street: “I noticed a wasp crawling around in the gutter. I always carry a collection vial, so I picked it up.” The wasp prompted an odd sense of déjà vu in Donovan. He looked for the tell-tale yellow band behind the eye, the black blaze down the snout of what should have been a German wasp. Instead, black crescents scribed each kidney-shaped eye, and he saw the diagnostic black anchor motif on its head.
“It was identical to specimens of the common wasp I’d collected in England.”
Donovan returned to New Zealand’s museum collections for a closer look. He found that several common wasps had been collected in Dunedin in December 1982, and one in Wellington in February 1983, “but they hadn’t been recognised as such”.
That April, entomologists found six common wasp nests around Dunedin.
Today, we’re pestered by millions of common wasps all over the country—we have the densest population of common wasps in the world—and Nelson Lakes is ground zero. Here, there are roughly 12 nests—maybe 10,000 wasps—in every hectare of beech forest. That’s an average: some surveys have found 30 nests in a plot the size of a football field. At season’s peak, researchers have calculated the mean biomass of common wasps in Nelson Lakes at 3.8 kilograms to the hectare—greater than that of birds, rodents and stoats combined. In high summer, they hum a ceaseless soundtrack.
Why do wasps enjoy such superabundance here? Because, for them, New Zealand is paradise. In their native northern hemisphere, they’re quelled by predators and competitors. But few followed them here, where they go about their industry impeded by little more than the competition for food. They are what ecologists call ‘density-dependent’; their numbers are controlled mostly by their own numbers.
There’s plenty of food. For wasps, New Zealand beech forests are bunkers of rocket fuel. Beneath the bark of many beech trees huddle, head-first, millions of tiny aphid-like scale insects. They feed on fluid in the tree’s phloem, but it’s so sugary that the insects pass some of it as excreta, through a white filament that projects from the trunk. At its tip forms a droplet biologists call honeydew. Taste it: it’s sweeter than syrup, and so loaded with energy that it powers whole ecosystems.
Nectar-bearing plants are scarce in beech forest, so tui, bellbirds and kākā depend on honeydew year-round, but never more critically than during the breeding season, when they use its energy to get themselves up to reproductive fitness. Geckos, and some insects, too, sip their sustenance from the scale insect’s butt.
Or they used to. Between September and February, wasps crave sugar, too, and by sheer multitude, monopolise the honeydew. Studies have recorded 370 wasps on a square metre of beech trunk, and each one can carry 15 microlitres of honeydew per trip. Over those five months, they’re reckoned to deplete the standing crop of honeydew by more than 90 per cent. Kākā breed intermittently at the best of times, but in wasp-ridden beech forests, year-on-year, they don’t even try. Tui ordinarily spend about 80 per cent of their time feeding on honeydew, but move out once the cost-benefit ratio crashes. Bellbirds tend to stick it out, but studies have shown they spend much less time and energy on flight, singing or social interaction.
A 30-year census of birds at Lake Rotoiti, which tracked the abundance of familiar species such as the bellbird, rifleman, grey warbler, tomtit and tui, straddles the years when common wasps arrived. Wasps are known to kill chicks in the nest, and the study found that below 1000 metres altitude, all five species had declined.
But there’s a still-greater harm. Wasps don’t sip honeydew: they know that if they nip the end off the scale insect’s anal tube, the nectar flows all the more freely. With every visit, the insect is nibbled closer to death. Wasps are trashing the engine room.
Meanwhile, the nests, and the numbers, keep ballooning. The queen’s days of manual labour are over: her exertions are solely devoted to laying eggs, producing ever more workers—sterile females born into indentured bondage. Initially, workers tend the grubs, but as they age, they go foraging for food, making trips of up to a kilometre. Unlike honey bees, wasps have no dance culture: they can’t direct their nest mates to a food source, so they simply follow one another in speculation. Neither do they possess the thriftiness of bees. Wasps don’t store honey or pollen for rainy days, so they’re forced to keep flying in them. Well-nourished wasps can operate in temperatures down to 2ºC.
Think of a wasp colony as a single, agglomerate organism. As a whole, it survives only by the singular labours—and physiology—of each of its parts. Queens, workers, drones, grubs; each depends on the others for survival, because no caste is built for autonomy. The guts of worker wasps, for instance, lack enzymes to digest the food they gather, so they feed it instead to the grubs, which have the necessary hardware. After digesting their meal, each grub regurgitates a blob of pulp, spare sustenance which they offer back to the workers. Behaviourists think this barter, called trophallaxis, is one of many clauses in a social contract that keeps wasp society humming.
So nourished, other workers concentrate on adding nursery rooms to accommodate the queen’s incessant reproduction. They excavate more chambers, then mix water and chewed wood fibre to add successive layers of comb, separated by a crawl space just sufficient to admit a worker wasp. The basement of a nest might hold 20 floors of comb, each supported by stiff struts and insulated by the sandwich of gaps—the working temperature of a wasp nest is 31°C.
Any female grub is an heir to the throne, but so long as the reigning monarch is healthy, her offspring cannot challenge for it—the queen emits a pheromone that prevents all grubs’ ovaries from developing. Instead, they’re preordained as workers. After hatching, they help to expand the nest chambers for a bit before leaving the nest on food-foraging trips. Anyone who insists hard work never killed anyone hasn’t asked a worker wasp: they live for about three weeks.
As summer stretches out, some grubs begin to hatch as fertile males, called drones. Two weeks later, out of specially enlarged worker cells in the nest’s dungeons crawl fertile females. These are the queens of autumn, and an average nest produces between 1000 and 2000 of them. They stay put in the nest, building up reserves of fat to fuel their long winter domicile. They suffer the drones until the first chilly portent of winter, then drive them from the nest. But the drones won’t go far: they mill about, waiting for the queens to emerge.
That final diaspora triggers a mêlée of mating. A queen will cache the males’ sperm in a series of tiny sacs called a spermatheca in her reproductive tract, keeping it viable until next spring, when everything begins anew.
Over a typical season, wasp nests grow as big as a basketball. But climate change has thrown another curve ball at the beech forest. Entomologists have known since the 1960s that around 10 per cent of German wasp nests survive each winter, giving them a head start come springtime. Such Lazarus nests pick up where they left off the previous autumn, with a workforce already good to go. This means they can grow, over successive years, to truly frightening proportions: the largest German wasp nest yet found in New Zealand was four metres high, and home to some four million larvae. In these year-on-year dynasties, the original queen is succeeded by several new ones in the second season.
In 1988, scientists discovered that three common wasp colonies had also survived a mild Nelson Lakes winter, although they hadn’t produced queens or drones in their second spring. At the time, entomologists believed common wasps could survive a winter only with good access to honeydew, but in 1993, three colonies lived through a Palmerston North winter with no honeydew in sight. The following year, a common wasp colony overwintered in Hamilton. As far as anyone knows, overwintering nests don’t produce any sexual offspring, but their major impact is on the surrounding fauna: so many wasps hunting so early in the spring can empty the larder that birds and other creatures rely on to sustain their own breeding.
In January 2017, Invercargill beekeeper Geoff Scott destroyed a common wasp nest, just outside city limits, 2.75 cubic metres in volume.
“It’s the biggest wasp nest I’ve seen or heard of in Southland,” he told reporters. This megalopolis had three entrances “the size of bowling balls”, he said. “We knew it was going to be huge.”
He estimated 30 or 40 wasps were commuting to and from the nest each second, putting the total number of adult residents in the hundreds of thousands.
Southland enjoyed a mild, dry spring in 2016, lending a flying start to the breeding season. Between November 2016 and mid-January 2017, Scott was called to at least five nests a week, one of which contained 30 queens.
“That would have been at least 20 new nests.”
Victoria University ecologist Phil Lester has tracked a trend in New Zealand wasp abundance against climate data going back 23 years.
“What we found was that, where it’s warmer and drier, especially in spring, then you’re likely to get higher wasp abundance in summer and autumn,” he says. “We’re likely to see more wasps in the future as our weather gets warmer.”
But that comes with a caveat, he adds.
“Under climate-change scenarios, some places in New Zealand are going to get wetter, and possibly even cooler.”
In such locales, he says, wasps will have a tougher time of it.
The language is important here: some summers may see record ‘abundance’, but that doesn’t necessarily mean a year-on-year increase in numbers, due to the wasps’ nihilistic breeding strategy. Because the vast bulk of wasps die at the end of each autumn, wasp populations don’t ‘cycle’, says Lester.
“So we can’t predict the abundance of wasps three, four or more years from now based on their current numbers.”
Observers have noticed one trend: wasp abundance seems to depend heavily on the previous year’s numbers.
“So, if there were lots of wasps last year, there are likely to be fewer this year. Conversely, if there were very few wasps last year, this year you might expect a bumper crop.”
For native biodiversity, though, this is just semantics—current abundance is catastrophic enough.
“A high density of wasps means high predation rates,” says Lester. “These things are huge predators; they harvest just about anything and everything.”
He’s not exaggerating. A 1993 study in scrub and pasture habitats near Hamilton calculated that wasps kill between 12,000 and 75,000 prey items—between 1.4 and 8.1 kilograms of invertebrates—in every hectare over the course of a season. So rapacious are they that some studies have reckoned the survival probability for some invertebrate prey species at next to zero. Lester is certain that wasps are responsible for the disappearance of the forest ringlet butterfly, now locally extinct in many former haunts. The smoking gun? Ringlets now persist only near the treeline, beyond the wasps’ altitudinal comfort zone.
“When we look at terrestrial ecosystems around the world,” says Richard Toft, an entomologist and wasp-control expert, “people like to think that the great herds of wildebeest are the big movers and shakers, but they’re not—it’s social insects.
“New Zealand forest ecosystems evolved without any social wasps whatsoever, so that when they finally arrived here, they found a paradise. They quickly became the dominant players in the ecosystem.”
And in the economy. Wasps routinely loot honey-bee hives, sometimes leaving them in ruins, costing New Zealand beekeepers around $9 million a year. Losses from unrealised honey production from beech-forest honeydew might come to $60 million annually. More broadly, their interference with bee pollination, which reduces clover cover in pastures, costs farmers another $60 million each year in higher fertiliser bills.
Each year, wasps cause an estimated $1.4 million worth of vehicular mayhem on New Zealand roads. Nobody knows how many New Zealanders get stung by wasps every year, but an estimated 1300 people seek medical attention annually, racking up a bill, according to DOC, for doctors’ visits, hospital stays, deaths and ACC claims of around $1.1 million. Allergy New Zealand says two to three people die each year from insect stings, and there could be more fatalities that haven’t been properly attributed.
Bob Brown doesn’t want me to be the next. “I think you should take one of these,” he says, proffering an antihistamine, “just in case.”
I pop it down, then flip the veil of my bee suit over my face and grope helplessly for the zips. Brown takes pity on me, zips me up, then dabs a length of masking tape over the Velcro closure. Then he winds coils of masking tape round my wrists, where heavy leather gloves meet suit, and again, round and round my ankles, at gumboot junction.
A peaked cap will, in theory, keep the veil from touching my face, which is really quite important. Feeling a bit like an astronaut, I waddle behind Brown, an entomologist at Landcare Research at Lincoln, as he heads for a nest of German wasps. He didn’t have to look far for this one. It’s next to a car park on campus, just a hole in the ground.
It’s overcast, and oddly chill for early March, but German wasps can deal with cool, and the entrance is a whirl of yellow motes.
Producing a garden trowel, Brown starts digging. German wasps are crankier than common wasps, and in seconds they’re all over him, and me. If we could only see it, the air between us would now be a mist of ‘alarm’ pheromones, released by the first wave of defenders, rallying their nest mates to the attack. They’re using an exaggerated wingbeat, too, a sort of harmonic siren that sounds across the colony.
I can hear that enraged buzzing as they crawl across my vision, and I watch them contorting their abdomens in belligerent yoga, trying to sting through my gloves. The air is roiling now, and I can’t help but dwell on the agony of those who’ve endured this kind of attack without protection.
Barry Donovan, the man who first noticed the common wasp in New Zealand, knows how badly this can go. On a January morning in 1981, he was retrieving comb from a German wasp nest on the outskirts of Lincoln.
“If I’m not back for morning coffee,” he’d only just joked to colleagues, “perhaps you should come and look for me.”
The nest was in an old, conquered bumblebee nest box, and as he lifted the lid, he remembers, he got stung on the cheek. Beekeeping suits in those days, says Donovan, were woefully leaky: “The veil must have flopped against my face as it sometimes could. I remember swiping at it, and that must’ve loosened the tie around my neck.” Two wasps got into the veil and stung him, one either side of his neck.
A scientist to the core, Donovan wrote up his experience in a notebook as soon as he could, and he reaches for it now.
“My writing from that morning is rather scratchy; I’m having trouble reading it, but it says: ‘Anaphylactic shock this morning from three stings at 9.00 am. Reaction almost immediate. Increase in heartbeat. Increase in temperature. Dizziness, blacked out 20 minutes. Loss of focus, vomiting.”
As he succumbed to the wasp toxin, Donovan had two options. Right across the road was the Lincoln Medical Centre; right beside him was a farm gate that led to a vacant lot.
“My brain had turned to fuzz,” he recalls. He took the gate. “I ran behind someone’s garage and collapsed there. I just had time to look at my watch before I conked out, and it was 9.00 am. I came to 20 minutes later; I know, because I checked my watch again.”
Luckily, the wasps had abandoned the chase. When he came round, Donovan hauled himself up on one elbow and threw up. “I couldn’t get up. I was trying to call out, but my voice was very weak. I could see clearly enough for 10 metres or so, but beyond that, it was a wall of mist. Suddenly, a woman loomed out of this mist, and I was somehow able to explain what had happened. Then she disappeared.”
Donovan faded in and out of consciousness, and the next thing he remembers was a doctor giving him an injection. “I recovered to a fair extent, and the woman helped me to her house, where I lay on her couch, puking into a bucket.”
According to his notes, he had his last chuck at 3.00 pm. “It was rather traumatic, but fortunately, I was a lot fitter back then.”
Donovan is one of an unfortunate few—maybe just three per cent of people—who react to wasp venom by going into anaphylaxis, an extreme form of allergic reaction. According to Allergy New Zealand, anaphylactic shock produces swelling in the throat and mouth, impaired breathing, pain, nausea, vomiting and “a sense of impending doom”.
Which may well be what Morris Stretch experienced on a February morning in 2012, when he felt the first few stings, and told his nephew to run. They were collecting firewood in front of their home near Sandy Bay, in the Marlborough Sounds, when they stumbled into a wasp nest. They fled in different directions. The nephew took stings to his back and arms, but was able, once the attack abated, to go back to look for his uncle. He found him dead.
Senior Constable Andrew Wilson of Havelock police told reporters at the time that Stretch had probably succumbed to thousands of stings.
“It’s hard to fathom how horrible that must have been.”
Looking at my hands and arms, I try to summon some hint of an idea. I’m crawling with wasps, and they’re all doing their best to sting through my suit.
After a few minutes, Brown reaches into the hole and draws out the nest; eight layers of comb. It’s a marvel. Creamy, eyeless grubs fill many of the cells—little zeppelins of protein—but from a few poke the heads of emerging males, greyish and matted. Even now, when all is plainly lost, workers are still rushing to defend them.
Brown points out the queen, and even to a novice like me, her primacy is palpable. She’s half as big again as any other resident, abdomen engorged by her burden of eggs. He points to her wings, tattered and threadbare from ceaseless scraping against the walls of her realm. This nest is her prison.
He scrapes off as many wasps as he can—it’s the grubs he wants—then gently lowers the nest into a plastic pail and seals it shut. He has to do this twice a week. Back at the lab, he has around a thousand hungry mouths to feed.
German and common wasps are not a big deal in their native lands, because they’re kept in check by a whole suite of parasites and pathogens that have evolved to exploit them. In New Zealand, however, they’re a very big deal indeed, because they mostly left those ecological handbrakes behind. Brown thinks that if we could reacquaint European wasps with some of their bloodsuckers of old, we could start to rein them in.
In Petri dishes on his desk, tiny copper-black wasps, not quite a centimetre long, are ranging over their plastic prison on spindly legs, their long antennae quivering.
“Ah, good,” says Brown, “some more have emerged.”
These are Sphecophaga vesparum vesparum, and he’s brought them back from the south of England, where they are the natural ruin of common and German wasps.
Sphecophaga wield both cloak and dagger: somehow, they can mimic the chemical aura of a wasp, emitting pheromones that shield them from detection and certain death. They walk undetected among their foes in the dark of the nest, seeking out grubs on the cusp of pupation.
“They lay an egg on the back of the larva’s head,” explains Brown, “just as the larva spins silk around itself, so it wraps the Sphecophaga egg up with it.” Soon unfolds one of nature’s most odious treacheries.
“The parasitoid larvae hatch and work their way down the back of the grub, then attack it from the bottom,” says Brown, “and this is what’s left…”
He calls up a computer image of an empty husk. Nearby grubs have taken on a rusty red hue—the blush of slow death by ingurgitation.
“This comb looks pretty well riddled,” he says, with satisfaction. It’s one he brought back from England in 2016, along with some adult Sphecophaga. The idea is to unleash them and their offspring (after due quarantine and diligence) into New Zealand, in the hope that they’ll continue their parasitic ways here.
This has been tried before. Sphecophaga were released in the 1980s—a total of 65 liberations—but they established only at Pelorus Bridge and Ashley Forest, where they had almost no effect.
That’s because they were imported from the wrong place, suspects Brown; they were from Switzerland, while our common and German wasps, genetic studies have shown, came from southern England or northern France.
“So, they may not have been the right ecotype to match the wasps we have here. It might be that Sphecophaga from continental Europe smell differently to those from England, which meant that the wasps could detect the Swiss Sphecophaga in the nest.”
Brown is testing his theory, raising his new brood on wasp comb such as we just excavated, to see if this English assassin can infiltrate where the Swiss one blew its cover. He points back to the image of the infested wasp nursery, where at least half of the cells have been parasitised: “These are queen cells, so each one of these is a queen that didn’t survive. And that’s the trick—knocking the queens down. They’re the ones you want to target.”
The number of queens a wasp nest might produce can vary wildly, he explains.
“One might have 200 queen cells—another one just metres away might have 2000. There’s huge variability in the reproductive output of these guys.”
The second of the German wasp nests we unearth is a shadow of the first, in both size and ferocity. The occupants put up little resistance, and the combs bear a pallor of lethargy. Brown thinks the nest is infested with a tiny mite, Pneumolaelaps niutirani, which he discovered in 2012. Either Pneumolaelaps was one of the few hitchhikers aboard those first, fatal incursions of wasps, or they’ve picked it up from bumblebees here. Whichever, Brown has noticed that infected nests—both common and German—tend to be less than half the normal size and vitality.
Like wasps, the mites feed on the saliva of grubs in the nest, so apart from stealing a bit of food, they’re not a biocontrol in themselves, but Brown thinks that some fungus they harbour as part of their normal gut flora may be anathema to wasps.
“We think the mites are a vector for some agent that’s harming or killing them,” he says. Like Sphecophaga, the mites could be using some pheromone to quell the wasps’ aggression—which may be why these wasps have little resistance to our nest-robbing.
Brown hopes to select among the mites for that pathogen they’re carrying, then breed them to deliver it, Trojan-like, deep into nests. Once the mites have been introduced, they’ll reproduce, says Brown: “At the end of the season, when the nests are collapsing, the reproductive wasps come out, and, right before they leave on their mating flight, the mites somehow hitch a ride on the queens.”
It seems that when a queen settles in for her long, cold hibernation, she may have a tiny bedmate—or dozens: “When we ask people to send us any overwintering queens they find, about a third are just loaded with mites.”
Wasps may seem invincible to us in New Zealand, but researchers point out that such parasites could have a bigger impact than we realise. As mites usually cause nests to collapse in their first few weeks, when flight traffic is already very low, it makes infested nests practically impossible to detect.
National Science Challenge funding has allowed for closer reconnaissance of the wasps’ defences, and a few weaknesses are starting to appear. A team at Victoria University, headed by Phil Lester, found some 200 different bacteria on common wasps—although only two dozen or so appear routinely—and a half-dozen viruses.
“For example, a lot of wasp populations here appear to have the same strain of deformed-wing virus as honeybees do,” says Lester. “They also have the Kashmir bee virus. In one study last year, at Nelson Lakes, every single wasp we looked at had that virus, yet we’ve taken samples in Belgium and other places, and we’ve never seen it in those European wasps. There are definitely different disease dynamics.”
Another control option is poison, but the trick involves finding one that will kill wasps, not bees. Around February, wasps switch from a diet of mostly nectar-based carbohydrate to protein—spiders, caterpillars, ants and bees.
“Protein demand is driven by the proportion of larvae developing inside the nest,” says Richard Toft. “That’s a critical phase. The nest is at some logarithmic population increase, and you’ve got these masses of larvae in there that need feeding. Carbohydrate mostly just fuels the individual, but protein gets shared right around the nest. That’s the time to get bait to them—good and early, so that you get the maximum effect. Obviously, it’s much better to kill off a whole nest, so there’s been a lot of research into exactly how and when that should be done.”
In the scrubby foothills behind Sandfly Bay, in Abel Tasman National Park, DOC biodiversity ranger John Henderson is lying in the dirt. The air, mere inches from his face, is a blur of little yellow comets—common wasps streaking to and fro. He’s found a nest right beside the park’s signature attraction, the Coastal Track. It’s high summer, and this week, about 3500 people will walk past this thronging colony. Most won’t even notice it.
Henderson assures me that, in three seasons of wasp monitoring, he’s not yet been stung at a nest. As I call out 60-second intervals, his thumb works the button of a counter, logging wasp arrivals and departures. We’re on the third minute-long sample when his winning streak ends: a wasp darts from out of the traffic and stings him on the hand. What had been a flight path of laser lines is starting to look more like a whirling cloud.
“They’re starting to get aggro,” warns Henderson. “You might want to step back a bit.”
I’ve already done so, but with impressive commitment, he resumes his count: 56 arrivals, 72 departures. The total is a de facto measure of nest activity.
“Anything over a hundred per minute is cranking,” he says.
He’ll repeat this risky census at the three other nests on his map—more intelligence in the war on Abel Tasman’s wasp scourge. It’s vital to know just where things are at, because Henderson is planning a counter-strike.
By late morning, he’s spooning dollops of budget-brand cat food into Petri dishes. It’s the third week of January, and he’s testing the wasps’ appetite, looking to catch the critical shift to protein Toft mentioned. He works quickly, because the testing protocol insists that foraging be sampled at peak activity, between 11.00 am and 2.00 pm.
Henderson sets out ten Petri dishes at five-metre intervals, then we dash to the next line, because the protocol also insists that the dishes be on the ground for an hour—no more, no less. He sets out four lines in all, then we backtrack, overtaking columns of day walkers and pushing our way to the front of long queues for the swing-bridges.
The number of wasps Henderson records on the cat food will tell him if their protein craving is peaking—whether it’s the moment to strike.
Turns out it’s not. The threshold is ten wasps per line, and we’re coming up short—just individuals here and there.
“At the peak of the protein phase,” says Henderson, “these dishes would be crawling with wasps.”
In early March, DOC makes its move. It’s an early start at the St Arnaud visitor centre in Nelson Lakes National Park, where poison bait will be laid, while a similar operation is taking place in Abel Tasman. Team supervisor Jennifer Waite is briefing staff and volunteers before they head out to load more than 1900 bait stations along the shores and at the head of Lake Rotoiti.
“It’ll be baking hot today,” she warns, “so the wasps will be active. Keep an eye out for nests. If you get stung, call back to base and let us know. Then call us back in ten minutes so we know you haven’t gone into shock.”
Along with radios, GPS devices, gloves, first-aid kits and a tub of bait, everyone gets an EpiPen, an automated hypodermic loaded with adrenaline, just in case. Waite points out wasp numbers aren’t quite so bad this season, possibly down to the wet spring last year.
“A lot of nests probably drowned. I’ve only been stung once this year—normally I’d get stung pretty much every day.”
She shows everyone how to handle the poison (“This is a really safe toxin, so long as you don’t eat it, or get it in your eyes”) and goes through the motions of dishing out two tablespoons, or 20 grams, of bait into a small plastic tray. These will be placed at 50-metre intervals, along lines 300 metres apart.
This year, there’s an extra $12,000 to lay bait further out, in the Sabine and Travers Valleys— two popular tramping routes in the park. The public stumped up the money via a crowdfunding campaign, Wasp Wipeout, run by the Nelson Mail, which raised more than $50,000 for control in the region.
It’s a 15-minute boat ride to the head of Lake Rotoiti, where senior biodiversity ranger Nik Joice and I will lay out bait in 30-odd stations either side of Lakehead Hut. It’s 9.30 am, so there’s only a faint hum of wasps as Joice spoons out a doughy, aquamarine paste. This is Vespex, the product of 15 years’ work by Richard Toft. It’s wasp-specific, and works on both German and common wasps.
After rejecting a raft of toxins, Toft and his Landcare colleagues turned to Vespex’s active agent, Fipronil, in the early 2000s. (Chemical multinational BASF holds the patent rights to the toxin, and donated $22,000 to the Wasp Wipeout campaign.) Fipronil has been around for ages, but Toft’s triumph was to work it into a protein matrix that wasps crave, and honeybees spurn. Apiarists are now among Toft’s biggest customers. Like most insecticides, Fipronil convulses an insect’s central nervous system, but unlike first-generation poisons, it is much safer to use around birds and mammals.
Some of those early poisons killed wasps at first contact, but that’s not ideal, says Toft. Vespex is a bunker bomb, going off only after a few hours, once it’s deep inside the enemy’s lair. Workers carry the bait back to the nest and feed it to the grubs, delivering a killing dose to their own. “It only takes minuscule amounts of that toxin to have a lethal effect,” says Toft. Once active, the end comes quickly. “The nest basically collapses overnight.”
Joice dabs the Vespex into a small plastic tray and places it inside a cheap plastic bait station, nailed at head height to a beech trunk. By the time he turns back to the bulk supply in the tub, wasps are crawling all over it. As the forest begins to warm, we pace out 50-metre intervals. If it’s a slow year for wasps, a busy one must be terrifying. While looking for nearby nests, I glance down to realise I’m practically standing on another—there are three nests within 20 square metres, and the canopy is humming.
As we near Lakehead Hut, I almost stand on something else—clumps of toilet paper and middens of human excreta.
“Yeah,” says Joice, “the toilets are full of wasps, so people won’t use them.”
The wasps prey on flies attracted by the loos, and I don’t even need to open the door of one to appreciate the trampers’ reluctance: it’s crawling with wasps, so Joice places a bait station close by.
About 90 minutes later, on our way back to the boat, we stop to check it. The wasps have practically emptied it already. There’s no need to top it up—that’s another virtue of Vespex. A tiny amount of toxin knocks out nearby nests, and because wasps take it so readily, it’s present in the environment for only a few days.
In 2015, Vespex trials at Lake Rotoiti reduced common wasp activity by 94 per cent, and at Falls River by 98 per cent. Those numbers are important: modelling has shown that lesser reductions do almost nothing to protect vulnerable prey species.
“I remember coming here in the early 1990s,” says Joice, “and the number of wasps was just crazy. Every square metre of ground would have wasps buzzing around—it was really horrible. When the wasp numbers get up around here, the hum of the wasps in the trees is all you hear.
“After we put the Vespex out, the next day you go into the forest, and you can hear the birds singing. It’s just amazing. It’s like throwing a switch.”
Vespex is the most potent wasp weapon yet, but it will never get rid of them entirely. There’s only enough money to treat the most popular tramping and camping areas, or critical honeydew reserves. In spring, an emerging queen flies well beyond DOC’s reach. That means Vespex is a job for life.
Because it works only when protein demand surges—in February or March—wasps have already depleted the honeydew resource. Honeyeaters such as tui, bellbirds and kākā aren’t much better off. But the poison does throw a lifeline to native invertebrates such as the forest ringlet butterfly.
But pesticides go only so far. Phil Lester is talking about nothing less than eradication. Under the National Science Challenge programme, he and colleagues at Auckland and Otago universities, Landcare Research and Plant & Food have mapped the common-wasp genome: “One of the final processes is annotating that genome to determine just which genes are which,” he says. “That sort of knowledge could facilitate a gene drive.”
A gene drive is, in a nutshell, a way to fast-track the spread of a certain trait in a population. Ordinarily, a gene has a 50/50 chance of expression, but gene drives use ‘selfish genetic elements’—sequences that promote their own transmission above the rest of an individual’s genome—to push the desired trait to the front of the queue. If you know which gene to attach them to, these selfish elements can make sure, for example, that all subsequent offspring are born male, or sterile.
“We’re not directly investigating gene drives as part of the National Science Challenge,” says Lester, “but that kind of tool will come on line in the next decade, and we’ll have the potential to eradicate species from New Zealand.”
But between potential and the Holy Grail of restoration ecology stands a dubious public. There is a history of qualm around anything ‘GE’, and tinkering with the whakapapa of any being—even an introduced pest—slashes at the Māori worldview. “There are lots of ethics to consider,” says Lester. “Just because we could use a gene drive against wasps, I’m not entirely convinced that we would.”
Gene drives would, ironically, flip New Zealand’s abiding paranoia about invasive organisms on its head—it was lax biosecurity that let these things in: we would be bound to make sure they never got back out.
“What happens if one of our wasps skips on a boat and goes back to Europe? We don’t want to be responsible for the eradication of these wasps in their native range.”
A more socially acceptable technique, says Lester, may be to simply isolate a mutation already present in the wasp mitochondrial genome—likely candidates would be mutations that compromise sperm count, or motility—then selectively breed it into a captive population for later release: the ‘Trojan female’ technique.
“So, you wouldn’t be touching the genome of the wasp, just exploiting existing genetic defects. We know there are existing mutations in the wasp genome that appear to be associated with small nest size and low queen production.”
But it would be a costly and complex solution, simply for the sake of sliver-thin semantics.
“You’d have to artificially rear lots of wasps,” says Lester, “and that would be a business facility all of its own.”
If New Zealanders were to sanction the use of gene drives on anything, though, it would probably be wasps, and at Otago University, Genetics Otago director Peter Dearden has already made a start, just in case they give the nod.
For now, his team is doing testing—under tight containment—on fruit flies, because we know more about the DNA of Drosophila than any other insect.
“We have over 100 years of genetic study to test some of our ideas,” says Dearden, “and to learn how to get them to work.”
Then, those techniques could be tested on a tiny wasp, Nasonia, “which is easy to contain and has been studied for a few decades. Nasonia shares a number of the genetic quirks of vespine wasps, so it’s a good model to work with.”
Just the same, there are many moves to play before the endgame: “There are lots of difficulties ahead to make a transgenic wasp—even more to make a gene drive. If it all works well—and I expect it not to—we might be able to achieve a transgenic wasp in two or three years.”
A gene drive system might take another six to ten years, says Dearden, but he points out that until we learn
how to raise and keep common wasps alive in containment—something that hasn’t yet been tried—that work cannot begin.
In mid-March, maybe a week and a half after John Henderson’s Vespex operation in Abel Tasman, I take a boat ride to Anchorage Bay, to check out how it went. I step ashore to the peals of bellbird, and even around the campground, with all its spilt food, there are no wasps to be seen. As I start out for Marahau, beech trunks along the track are already glistening once more with honeydew, and honeybees are gorging on it. In just over 11.5 kilometres, I count five wasps.
Such peace is a powerful proposition. To think that we could, one day, be rid of wasps and their ransacking omnipresence; that for beekeepers, holidaymakers, forestry workers, the world might return to something more benign; that our beech forests might once again work how they should; that we might walk through them without having to watch our step, and not strain to hear a tui over that tyrannical hum; that native insects might hatch to an even chance of adulthood, that we might see the forest ringlet return.
Science holds that tantalising promise. All we have to do is think straight, and get it right.