The wasps' hum, the white noise of the forest, is a constant reminder that they — the foreign invaders — are winning.
They are having a devastating impact on our native birds, bats, lizards and insects, exploiting the most valuable food sources of the forest and entirely altering New Zealand’s natural biodiversity.
These wasps are also a serious threat to people, delivering painful stings that can cause life-threatening allergic reactions and — in extreme cases — death.
The German wasp (vespula Germanica) and common wasp (vespula vulgaris) have been described as New Zealand's most abundant and devastating invertebrate pests.
To appreciate their impact on the environment, and our native species, we first have to understand how many wasps there are.
Studies have found that, at their peak, there can be up to 40 nests per hectare of beech forest.
A nest can produce thousands of queens and thousands of workers, and there are about a million hectares of beech forest in the South Island.
Based on these figures, there could be up to 40,000,000,000 (10 zeros) wasp queens in the beech forest at the height of summer, and many more workers.
Insect ecologist Richard Toft says the impact of that amount of wasps on the ecosystem has “got to be catastrophic”.
“We have a lot of talk about rats and stoats and mice and their impact on systems.
“But put wasps in those same forests, the biomass of wasps exceeds the combined biomass of all the rats, all the mice, all the stoats and all the birds.
“You simply can’t add that amount of biomass into an ecosystem and expect it to have no impact.”
Common wasp vespula vulgaris
The common wasp arrived in the 1970s, but Toft says genetic testing suggests there were up to 10 separate introductions.
Despite arriving later, the common wasp has largely displaced the German wasp in beech forests.
German wasp vespula Germanica
In New Zealand, these wasps had no natural predators, few competitors, mild weather and an abundance of high-quality food.
By declaring war on our native species, the invaders flourished in their new home. New Zealand now has the highest densities of these wasps in the world. And the Nelson-Tasman region has been declared the “wasp capital” of New Zealand.
The wasps are drawn to the South Island beech forest by honeydew, a sugary drop excreted by scale insects that burrow into the bark of the beech tree.
Honeydew is an important food source for native birds like tui and bellbirds, as well as some lizards and insects.
However, each summer, vespula wasps consume about half of the beech honeydew, according to a study by the Department of Conservation.
When the wasps are done with the energy-rich honeydew, they turn their attention to insects.
This not only impacts directly on insect populations, but it also removes another vital food source for birds.
Wasps don’t discriminate on their source of protein. They have been known to attack, kill and eat fledging native birds and bats.
“There’s nothing that they won’t eat in the environment up here,” says Friends of Rotoiti founding member Bryce Buckland.
“They’ll eat everything — stick insects, baby birds — everything. They just clean everything right out. 100 per cent of insects won’t survive in a wasp environment.”
Buckland, who has been involved with wasp control around Nelson Lakes National Park for about 16 years, compares the beech forest to a supermarket.
“If you can imagine if you went to your local supermarket and someone’s pinched all the best food, that’s pretty much what’s happened with wasps. They’ve pinched all the best food and put nothing good back into the environment again.”
So why does this matter?
Like possums, rats and stoats — New Zealand’s most familiar pests — wasps are contributing to the decline of our native species and the degradation of their environment.
“It seems likely that these wasps are causing a much reduced abundance of our native flora and native fauna,” says Victoria University insect ecologist Professor Phil Lester.
The forest ringlet butterfly
“There’s a bunch of us that suspect that wasps are driving things like the forest ringlet butterfly to extinction.”
The introduction of foreign wasps has also impacted on the ability of people to enjoy the outdoors in summer.
Picnics, bush walks, and even chores around the home like gardening and lawn-mowing have turned nasty because of wasps.
If disturbed, German and common wasps can deliver painful, venomous stings that causes some people to have allergic reactions, known as anaphylaxis. The symptoms range from pain, swelling and shortness of breath to death.
“For those people, it’s pretty scary,” says DOC Nelson Lakes senior biodiversity ranger Nik Joice.
“They say that when you do have a really bad reaction you have a sense of dread and fear that you’re going to die.”
But just the presence of wasps — their incessant drone — can ruin a day in the outdoors.
“If you’re a hiker in late summer-autumn in beech forest then you are very aware of wasps. You sit down and try and have your lunch and you are swamped. It’s very easy to walk on a nest in those circumstances,” Lester says.
“Compared to what it was in a land without wasps, that’s a dramatic loss of enjoyment and pleasure.”
Beyond the direct effects on people’s health and wellbeing, wasps are also a drain on the economy, impacting on forestry, farming, bee-keeping, vineyards and more.
A Department of Conservation study, published last year, estimated that wasps cost New Zealand about $130 million a year.
Despite the serious, widespread impacts of introduced wasps, the government declined to include them along with rats, mice, stoats and possums when it announced plans to make New Zealand predator free by 2050.
“When people worry about rats and stoats and possums, wasps are actually, on my list, either number one or two around rats for the worst destruction of bird species — and those are the species we’re trying to save,” Buckland says.
This is why the Nelson Mail and Stuff are partnering with the Department of Conservation and local conservation groups on Wasp Wipeout — a community-led project aimed at significantly reducing German and common wasp populations in the Nelson-Tasman region this summer.
Wasp Wipeout is supporting existing wasp control operations through crowdfunding to enable them to continue this summer and, in some cases, expand.
People can also register their interest in specific projects, or take the DIY approach by doing their own wasp control operation in their community, street, or backyard.
“The fact that we live in such a gorgeous area surrounded by three national parks, we really should be getting involved in how we protect those areas and how we enhance the quality of our life here,” Nelson regional editor Victoria Guild says.
Environment minister Dr Nick Smith says Wasp Wipeout is an “incredibly ambitious project” that complements the government’s Predator Free 2050 goal.
“It's part of a broader revolution taking place in New Zealand into having a real respect for the species that are unique to our country, rather than our ancestors who tried to create another English countryside,” Smith says.
"We've proved this year with the successful completion of the great white butterfly eradication that the community, with smart science, can actually eliminate insects.”
The wasp control method that has been adopted by conservation groups and approved for public use is the protein-based bait, Vespex.
Wasp bait Vespex Photo: Richard Toft
Developed in Nelson by Richard Toft, managing director of Entecol, Vespex has been remarkably successful in wiping out wasps.
Trials in five locations across the South Island, including Abel Tasman and Nelson Lakes national parks, last year achieved between 95 and 100 per cent wasp eradication.
Joice says Vespex is an “amazing tool” for wasp control in the Nelson Lakes area.
“When the wasp numbers get up high here the hum of the wasps in the trees, it’s all you hear.
“We put the Vespex bait out and the next day you go into the forest and you can hear the birds singing. It’s just amazing. It’s like a switch.”
Nelson regional editor Victoria Guild says the goal of Wasp Wipeout is not eradication, but to create a “corridor” around urban and popular conservation areas that is wasp-free.
“It’s really crucial for a project like this that everybody’s on the same page at the same time working towards a common goal.
“To be able to target one pest at one time and give it a really good, hard shot — that’s where we can make a difference.”