The Nelson Mail and Stuff are today launching Wasp Wipeout, a community-led conservation project that aims to significantly reduce German and common wasp populations in the Nelson-Tasman region this summer. To help explain why, Jonathan Carson reports on the devastating impact of vespula wasps on our environment, people and economy.
In the height of summer, you can hear it — the drone of vespula wasps ransacking the forest.
It drowns out the songs of native birds — tui, bellbirds, kaka.
It puts fear into families trying to picnic on the stony shore of Lake Rotoiti, trampers venturing into the bush, and mountain bikers hitting the trails.
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 frequency of people being hospitalised or even dying … puts wasps as one of the most dangerous insects in the country.” – Victoria University insect ecologist Professor Phil Lester
“The most hated pest in the country. Nobody has a good thing to say about them.” – Bryce Buckland, Friends of Rotoiti founding member
A villain of the forest
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 (40 billion) 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.”
The German wasp arrived in New Zealand soon after World War II, most likely on a ship carrying aircraft parts from Europe. It was first sighted near Hamilton in 1945.
A newspaper article at the time reported that “it appeared that the pest was now established in New Zealand and could not be eradicated”.
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.
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.”
“These things are super predators.” – insect ecologist Richard Toft
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.
“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 a painful sting with an injection of venom 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.