Wasps are a pain in the… wherever they sting you. We all know that. But some experts believe there are parts of the country where they’re even more destructive to wildlife than stoats and rats. Matthew Pike asks if we’ve ignored these demons of the forest for too long

Annoying. Irritating. Pesky. These are three of the tamer words we use to describe the infuriating (there’s another) experience of trying to eat a hard-earned lunch while surrounded by a swarm of yellow and black blighters.

In late summer, there are certain parts of the country where, try as you might, they’re just impossible to avoid. Once you shake one off your hand, there’s another on the rim of your drink bottle. Then another gets caught in your hair, which leads to the strained, frantic buzz of a wasp trying to escape just inches from your ear.

The situation is unrelenting and quickly becomes unbearable, leaving you with no choice but to finish your jam sandwich on the move. The view you were hoping to savour will have to wait until later in the year. The river into which you were hoping to dip your feet will have to continue babbling without you – not that you could hear that babble over the droning din of a million flying insects.

Anyone who’s tramped through forest in the northern part of the South Island and various forests in Northland and around Auckland will have experienced this. There are parts of New Zealand where the wasp density is greater than anywhere else in the world.

The beech forests covered in honeydew (a sugary liquid secreted by aphids and some insects), and kanuka and rata forests are just heaven for them. New Zealand has no native social wasps (the only native species are solitary). So over the last 70 years two invasive species – first the German wasp, then the common wasp – have become dominant, feeding on the bucket loads of honeydew found in forests and with no natural predators.

The upshot is that between January and May each year, there are certain forests in which they are simply everywhere. This is more than just a nuisance. It can be dangerous, particularly for trampers who don’t stick to the paths.

“The problem’s more prevalent with people who head off track,” says DOC entomologist Eric Edwards. “They’re far more likely to step on a nest or get very close to a nest. Wasps won’t build their nests on a hardened track.”

No-one knows this better than keen tramper Lew Shaw. Shaw, who lives near Ashburton, in Canterbury, got attacked four years ago in Black Lizard Gully, on the slopes of Mt Somers.

“I climbed up a small waterfall with my partner Maggie and we’d only been in the gully for five or 10 minutes when I decided to go through a patch of scrub. I stuck my boot on a rotten log and, before I even saw them, I felt them sting me through my polar fleece jersey.”

Unbeknown to Shaw there was a wasp nest inside the log and he got stung a couple of dozen times on his body, arms and face. Shaw’s a member of the Mt Somers Walkway Society which will launch a poison bait programme this summer to ease the number of wasps in the area. But he knows there’s only so much the group can do.

A wasp nest in Nelson Lakes NP

“It’s labour intensive,” he says. “We might poison a section of track and 100m away there could be another nest totally unaffected.”

But his experience in Black Lizard Gully is enough to inspire him to try and curb the problem. “I was lucky,” says Shaw. “It was a bad cold compared to what it could have been – it could have been so much worse. I was lucky not to have an anaphylactic turn.”

And it’s that sort of reaction which make wasps potentially deadly to those in the backcountry. DOC ranger Nik Joice, who’s based at Nelson Lakes – an area renowned for its wasp problem – says there’s a case of someone going into anaphylactic shock in the park every couple of years.

“People who get multiple stings are normally fine – the worst thing is the itching,” he says. “But occasionally a person will have a bad reaction. We carry adrenaline kits with us in the field, which can reverse the reaction.

“One of our workers had a bad reaction within 10 minutes of being stung – he gave himself adrenaline with an Epipen and the rescuers in a helicopter gave him three or four lots of adrenaline until the reaction reversed.” A bad reaction can include swelling, tight chest, shortness of breath, persistent sneezing or coughing and difficulty swallowing.

Another area where the wasp problem is particularly severe is Waitakere Ranges Regional Park. Nick Waipara is an advisor for biosecurity for Auckland Council, which manages the park, and says the number of wasps has got to the stage where he’d advise some people to stay away at certain times.

“If I was allergic to wasp stings I wouldn’t go into the Waitakeres without an Epipen in high wasp season,” he says. “I hear stories of people not enjoying the park in high season and, if you are sensitive to wasp stings, you’re in great danger.

“There have been periods where it’s been too dangerous for our team to be in the bush doing trapping and research – the situation’s prevented them from working there in late summer.”

Ecologists fear the impact wasps have on the country extends far beyond the danger to humans. We’re all familiar with the effect rats and stoats have had on our native birdlife. But Jacqueline Beggs, who’s been studying the effects of wasps on the environment since 1984, believes they should be placed in the same bracket of threat.

“When people talk about ‘pest free New Zealand’ they tend to mean ‘vertebrate pest free New Zealand’,” says Beggs, who’s the associate professor in ecology and entomology at the University of Auckland.

“Vertebrates always get more focus than invertebrates. As an ecologist, I’d argue that, although vertebrates have a great impact, wasps can have a far greater impact in some forests.

“They act on a whole range of levels – they’re predators that kill nesting birds and insects, and consumers of vast amounts of honeydew.”

Beggs argues that the effects wasps have on birdlife may not be as direct as the effects of stoats and rats, but they certainly add significantly to the conservation problem. Eating insects and honeydew deprives birds of their food source. “Sugar also has an important impact on the nutrient cycle of the forest,” she says. “So the wasps affect everything right across the spectrum – from decomposition and the nutrient cycle to predation.”

Scientists measure levels of infestation in terms of biomass – the grams of organism per hectare. “We’ve done research estimating the biomass of wasps compared to other predators,” says Beggs, “and in forests of high wasp density, the biomass of wasps is equivalent to all other predators put together.”

Eric Edwards agrees that wasps are one of New Zealand’s major pests.

“It’s up there with the vertebrate pests,” he argues. “There’s no question wasps are in the top 20 animal pests in New Zealand; I feel they could be in the top 10.

“It’s partly because of their impact on nature and partly for their impact on people – possums and stoats don’t sting you.”

Wasps collect bait to take back to their nests in Nelson Lakes NP

And to make matters worse a new aphid has been discovered. The giant willow aphid lives, as the name suggests, on willow trees but also on poplars. It was first discovered last year and the species actually produces honeydew, meaning, should the aphid’s population explode, wasps could become more widespread.

“At the moment, the aphids are in low abundance,” says Edwards. “But their season matches the wasp season. There could be really high infestations and the wasps could take advantage.

“I think there’s a good chance this could happen – over winter it’s not a problem, but over summer it flares up.”

So, what’s been done to solve the wasp problem? Well, to put it bluntly, not a lot. There has been precious little money invested into research. Wasp numbers are colossal and there can be up to 20 nests per hectare with wasps never heading more than 100m or so from their nest. So ground bait can only be of limited use. The wasp fighters don’t have their version of 1080 and are still years away from finding the tools for the job.

Wasps are a hassle not just to trampers, but to all sorts of primary industries including farming, bee keeping and wine growing. Yet funding to combat wasps has always taken a back seat – a fact Jacqueline Beggs blames on the insect being everyone’s second problem.

“Wasps are a significant problem to a lot of groups, but are not the main problem,” she says. “Everyone stands back and says ‘they’re not the number one priority’, but if you cost it out nationally, what does it come to?

“DOC acknowledges it’s a major issue but it has so many major issues and, with declining resources, what are they supposed to do?”

The wasp issue briefly came to the fore in the late 1980s when the population of the common wasp exploded. “Politicians threw a million dollars at it for one year,” explains Beggs. “What can you do in one year? It was a brief flash in the pan.”

The effects of wasps are also extremely difficult to measure. In forests with multiple pest predators how can you tell how much impact each is having?

The best information we have has been gathered from Nelson Lakes, where bird populations were measured since the early 1970s – before possums or common wasps lived there in any great number.

“Any change since then,” explains Beggs, “is likely to have been because of a new introduction and results showed an on-going decline of tui, grey warbler, bellbirds, tomtits and riflemen. This is probably attributable to a combination of possums and wasps.”

Field experiments have also shown that invertebrates such as caterpillars and spiders have virtually no chance of surviving for a year in areas where wasps live in high density. “We know the impact on invertebrates is very high and we know the wasps are monopolising the honeydew supply for three months of the year,” says Beggs.

But there hasn’t as yet been enough hard evidence to convince the Government to make a serious investment into the issue and, without the investment, there can be no hard evidence. Wasp numbers were measured at various South Island locations for 20 years, but a few years ago Landcare Research pulled the plug on funding for this too. Now we have no records of wasp numbers.

But before waving the white flag and conceding defeat to this most unpleasant plague, there’s a glimmer of positive light perched on the horizon.

Nelson Lakes has long been regarded as ‘wasp Mecca’ – a sugary heaven where the sky is the limit regarding how high their population can grow.

But in recent years rangers there have noticed a downward trend in wasp numbers. It’s only anecdotal (again, there isn’t the funding to measure this), but they have noticed a change. This could just be due to poor spring weather preventing soaring numbers, but Nik Joice believes there’s more to it than that.

“There’s been research in Canterbury where they’ve discovered a mite,” he says. “They had a couple of nests in the lab that collapsed and discovered these mites on the wasps.

Wasp expert Jacqueline Beggs argues that wasps have a greater impact than rats and sloats in some forests.

“We’ve found the same mite on queen wasps in wood piles over here this winter.” Very little is known about the mite – it hasn’t been discovered anywhere else in the world. Joice admits it’s only speculation but there does seem to be something happening.

“Normally, after a low wasp year, you have better quality queens, but that doesn’t seem to be happening at the moment. Something’s going on – we’re just not sure what it is.”

It’s a ray of hope to which many are now clinging. It appears the primary industry community is starting to take an interest in tackling the issue. So this year the Sustainable Farming Fund has given a grant to the Vespula Biocontrol Action Group, which has contracted Landcare Research ecologists Ronny Groenteman and Bob Brown to research the mite’s effectiveness at stemming wasp populations.

“It’s about reuniting wasps with natural predators,” says Groenteman. “The mite is already found in New Zealand. We may need to bring in more than one agent down the line, but we’re starting with what we already have.”

But Groenteman warns that it’s early stages and research like this takes a very long time. “There’s lots we need to be very careful with,” she says. “It’s very slow to develop a biocontrol programme. There are several steps, such as testing safety – making sure the mites only attack wasps, not bees. It takes a long time to test these things in a controlled environment.

“We also need to establish enough of a population and it can take years to build up high enough densities to have an effect.”

Groenteman says there needs to be much more funding into wasp research: “We’ve been fortunate – we’ve received funding but there definitely hasn’t been enough investment into this. There won’t be one silver bullet – we need to invest in as many tools as possible.”

Other tools could one day include developing carbohydrate baits specific to wasps, or using pheromones as species-specific attractants, which would attract only wasps to poison stations, while all other insects avoid the poison.

Several toxins have been trialled in New Zealand. One, in particular, has been proven successful in low concentrations and is currently being tested in Nelson Lakes over 1000ha.

“The difference is incredible,” says Joice, who’s monitoring the results of the trial. “One of the first things you notice is that you can hear the birds singing again – not just the hum of wasps.

Wasps love the sweet taste of honey dew. Photo: Mike Taylor

“Monitoring shows that 90 per cent of wasps totally die out.”

Toxins that have been trialled against wasps include mirex, 1080, fipronil and sulfluramid. There is currently no funding into pheromone research.

In an age of numbers, someone needs to work out how much money wasps cost the economy; be it through medical treatment for stings, helicopter rescues, destroyed grapes and crops or the mass slaughter of bees.

Only when this figure is realised can we hope for something to be done about it. Until then, when tramping among sugar-coated trees in late summer, we’ll have to continue eating our jam sandwiches on the move.