I’d just finished a delicious four-course dinner at Kauri Cliffs, a windblown New Zealand lodge surrounded by 6,000 acres of forest and rolling coastal farmland in the North Island’s Northland region. Now, I could sit back with a tumbler of single malt Scotch, thumb through glossy magazines in my cosy bungalow or queue up a movie – all more-than-suitable comedowns from a day spent strolling and taking a horseback ride to the beach.

On the other hand, I could go shooting possums.

I saw this activity listed – alongside golf and tennis – on the Kauri Cliffs website when I first booked. Not quite believing it, I checked with the front desk when I arrived. Yes, they assured me: a nocturnal possum hunt was definitely on offer.

After dinner, I found Darcy Rhodes, the gamekeeper and resident possum expert, waiting in the hotel’s pebbled drive. My hunting guide for the evening was a 30-something local guy in jeans. His left arm was in a cast. “Motorbike accident,” he shrugged, and we hopped into his mud-spattered pickup.

Our first stop was the spacious shed that is the closest thing Rhodes has to an office. We picked our way through seed bags and farm machinery to a freezer in the back – out of which he pulled a stiff, black object the size of a large housecat. It was a possum, teeth bared, petrified into a pose of snarling fury. “Look at those claws,” Rhodes told me. “You can’t treat ‘em like a teddy bear, see? They’ll take your fingers off.”

I don’t own a gun. I had never hunted before, unless you count clay pigeons and tin cans. I wasn’t particularly comfortable shooting wild animals – never mind at night and in a place about as far from home as I could possibly get.

On the other hand, I was up for an adventure. Particularly for one that, according to the hotel, actually helped the environment: New Zealand’s possums are one of the several armies of non-native creatures that have decimated the country’s indigenous plants and animals, including entire canopies of indigenous totara and kohekohe trees, the kiwi and the blue-wattled kokako bird.

Rhodes armed me with a .22 and – his grin widening – a 12-gauge shotgun. “That one takes no prisoners,” he quipped.

I think we both knew I’d end up using the shotgun.

Furry invasions

Rhodes’s official title is not gamekeeper; it is “pest-control manager”. And when he’s not taking guests out for night shoots – which he only gets to do about once a week – he is trapping and baiting all sorts of unwanted critters at Kauri Cliffs. Possums are the main enemy, but so are stoats, weasels and hares, as well as feral cats and pigs – all of which were introduced when Europeans arrived in New Zealand in the late 18th Century.

Exclusive of these invasive species, New Zealand is a naturalist’s dream, with primeval trees that look like scenery from the movie Jurassic Park and a shrinking panoply of charmingly old-fashioned birds, including the kiwi and a flightless parrot known as the kakapo. And since many of these endemic species evolved in isolation on the islands for millions of years, they are particularly vulnerable to imported predators.

Brush-tailed possums arrived from Australia in 1837, brought by British colonists hoping to use their pelts to launch a fur trade; the colonists ended up launching an animal invasion instead. Today, possums feast on bird eggs and chicks, and eat up to half a pound of new growth foliage a day. At Kauri Cliffs and elsewhere, possums also compete with birds for food, a contest in which their size and ferocity give them a distinct advantage.

Unlike Australia, meanwhile, New Zealand has no deadly natural predators. “Here, they only got me to fear,” as Rhodes put it. “And you.”

Havoc on ecosystems

New Zealand isn’t alone in its battle against invasive species. In North America, exploding populations of Burmese pythons, feral pigs and the beaver-like rodent known as a nutria (introduced in the Gulf Coast from South America in the 1930s for a short-lived fur trade) are wreaking havoc on ecosystems. Researchers and conservation groups are calling the infestation of lionfish (which established themselves in the Atlantic in the early 2000s after being released into the ocean by Florida pet-owners) the worst marine invasion in history.

Occasionally, efforts to curtail these species dovetail with the tourism industry. In Chicago, chefs have turned Asian carp into ceviche and chowder in an attempt to curb the rise of the plankton-devouring species, which has spread to Great Lakes since escaping from US fish farms in the 1970s. The World Wildlife Fund offers a commercial tour in Palau, Micronesia on which snorkelers can help their guide remove the invasive crown-of-thorns starfish, which every day eat their weight in coral polyps from fragile reefs.

Overall though, the inroads have been negligible. Efforts to rein in the lionfish seem to be the only initiative generating much interest beyond the local level. Dive shops in Florida and the Caribbean are asking clients to record where they find these ravenous consumers of native fish, and are encouraging divers to go spear fishing for them. Conservation group REEF, which is based in the diving Mecca of Key Largo, Florida, introduced “derbies” in 2009. Since then, these competitive hunts – with prizes awarded for the most fish killed – have removed an estimated 12,000 lionfish.

While not every casual visitor wants to wield a spear, it can be a more appealing prospect than the average eco-tourist might imagine. “I think we all have this innate hunter-gatherer in our genes somewhere that is typically suppressed,” said Lad Akins, REEF’s Director of Special Projects. “So often in conversation we’re told what we cannot do, where we cannot go, but here’s an instance where we’re saying here’s something you can do. We want you to go out and take something.”

“Some people think we should just let nature take its course,” Akins added. “Our general response to that is that this isn’t a natural phenomenon. We caused this.”

Possum o’clock

Driving over double-track to the outer boundaries of Kauri Cliffs, Rhodes scanned the grounds using a high-powered flashlight. Our first possum soon came into view, turning its thick flanks to us as it raced away. Rhodes cut the engine; by the time we got out, the animal had clambered about 12m up a tree. Its orange eyes gleamed eerily in the night.

“Best to hit it under the chin,” Rhodes murmured. I had dreamed of executing the perfect shot. Instead, I couldn’t even get the scope to focus.

“You try it,” I said to Rhodes, handing him the gun.

He calmly rang off two shots. The possum started wobbling on its perch. Rhodes fired again, sending it crashing through the branches and landing with a whump.

Immediately, a second possum made a dash some 6m away. This was within my range, and I managed to stop it with one shot. “Got him!” Rhodes shouted.

I felt a nervous, almost caffeinated buzz as we examined the results. Rhodes considered his carcass trophy-worthy and threw it in the truck-bed. We left mine where it lay. “Hawks will clean it up,” he said.

I killed a half dozen more possums that night. For each, I used the shotgun, which demanded nowhere near the same precision as the rifle and did far more damage. Rhodes led us over to most of the victims after they went down and had me finish them off if they were still twitching. I felt invigorated – and sickened. An hour of carnage was enough for me.

At Cape Kidnappers, the other Kauri Cliff lodge on the North Island, the owners have spent an enormous amount of money (they wouldn’t tell me exactly how much) on a 10km fence. Unlike the simple, wire livestock fences at Kauri Cliffs, this one is state-of-the-art: it is too deep to be burrowed under and has a curved steel capping to keep animals from jumping over. Thanks to such sophisticated protection from predators, the property’s nature reserve is home to several dozen kiwis.

Here, a visitor can go into the woods accompanied by a naturalist who will use a radio transmitter to find one of the endangered birds. You’re even allowed to pick it up and cuddle it.

This sunnier, fuzzier side of eco-tourism is the one most often talked about – and we amateurs are not often offered a ride over to the messier, nastier side of the same coin. But if I ever am invited to do so again, I know I’ll accept.