A nondescript field in Cromwell is the world’s first—and only—nature reserve dedicated to the protection of an invertebrate.
It doesn’t look like your average nature reserve. A balding paddock alongside a major road, cars sweeping past. The only clue is the green-and-yellow Department of Conservation sign.
This patch of sunbaked grass is the home of the critically endangered Cromwell chafer beetle, Prodontria lewisii, a plain brown beetle that lives underground. Today, it’s the scene of a long-running scientific ritual.
A small army of DOC rangers and AgResearch scientists arrives, prepared for a day of digging beneath the Central Otago sun: wide-brim hats, jumpsuits, gloves, kneepads. Every December, for more than 15 years, they’ve come here to count beetle larvae.
DOC senior biodiversity ranger John Keene smears sunscreen on his face as he briefs the beetle counters. The sampling area is striped with lines of measuring tape and marked with fluoro spray-paint at regular intervals. A digger starts up with a puff of fumes.
“We ready to dig some holes?” says Keene.
The process involves sifting through 672 soil cores—long tubes of dirt extracted by a digger fitted with a coring attachment, reminiscent of an elephant’s trunk. It swings from one spray-paint mark to the next, twirling into the ground and plopping a soil core onto a canvas mat, where the dirt collapses into a dry, sandy heap. It’s then sifted through by hand.
The larvae we seek look much like any other grub: silvery, about a centimetre long, with ginger-coloured heads. We’re counting larvae rather than adult beetles because this is a more reliable method for estimating population-density changes over time.
Cromwell chafers are a strange lot: nocturnal, flightless and, like the paddock they inhabit, very plain—reddish-brown, scarab-shaped, about the size of a walnut.
They’re also highly specialised, inhabiting only a specific type of shallow sand, found in the windblown dunes of the Cromwell Basin.
Scientists believe the Cromwell chafer’s natural range may be one of the smallest known of any animal species, having never exceeded about 500 hectares. Today, the beetles’ home range has been reduced to a fraction of that.
The construction of the Clyde Dam and the formation of Lake Dunstan in 1993 flooded much of their habitat. The expansion of a golf course wiped out one population and land-clearing for housing whittled down the available land even further. Cromwell chafer beetles are left with just 81 hectares—a triangular slice of grass-strewn sand, hemmed in by a road, a forestry block and a motorsport park.
Today, the counters are panning for beetle gold. Dry lichen crunches underfoot as people traipse up and down the line. Calloused hands tease apart grass roots and eyes scan the broken dirt for any signs of movement. Barbara Barratt, principal scientist at AgResearch, takes up the rear, outfitted in a yellow-brown jumpsuit that blends into the sun-tanned landscape. Clipboard in hand, she’s noting down the results from each core.
“We’re recording all the invertebrates that we find,” she says. “We’re interested in everything that’s here, in case there are any interactions between other species and the chafers.”
Most of the cores are devoid of life, except for a couple of house ants or mites.
Then, 15 minutes in, we strike gold: a larva, moving fast across the soil-strewn mat. Barratt picks it up, cups it in her palm and squints at it through a hand lens. It’s a Cromwell chafer. A buzz of excitement sweeps along the line and counters abandon their cores to have a look.
Chafer beetle larvae spend several months buried in sand, chewing on tussock roots and developing through three stages called instars. Then, they transform into pupae—a stage of their lifecycle which has never been observed in the wild—and after another three or so months, break out of their stiff, curled casing. As adults, they spend their days cocooned in burrows up to half a metre underground, emerging on spring and summer nights to mate and eat scabweeds (Raoulia)—low, dense plants that form cushioned mats, like moss.
At the end of the day, counters return with dusty faces, hands and knees and the humming of the digger fades away.
The Cromwell chafer count for this year: one.
In the late 1960s, entomologist Charles Watt searched high and low across Central Otago for other populations of Cromwell chafer beetles, to no avail. He finally concluded that the species’ extreme specialisation meant it was “in imminent danger of extinction”.
Watt began to study the ecology of the beetle and to campaign for its protection in the face of urban development and dam-building. His enthusiasm inspired action among Cromwell locals, with two women constructing pitfall traps in 1975 and 1976 to capture and translocate beetles from an area slated for housing development. In 1979, the Cromwell Borough Council fenced off the reserve, southwest of the township, on Watt’s recommendation.
“He got the local people really interested,” says Barratt. “They felt proud to have this rare and endangered species on their back doorstep. In those days, people were finding them in their gardens, and he was encouraging them to take them to the reserve area and drop them over the fence, and they willingly did that.”
In 1983, the area was officially declared a nature reserve—the first in the world created specifically for an insect.
But life in this protected corner of the world hasn’t been easy. In 2004, a plague of European earwigs struck, and in 2012, large numbers of redback spiders, an import from Australia, were recorded.
“We had schoolkids observing the count and they were the ones who first spotted that there were quite a few redback spiderwebs,” says Barratt. “Then we found cadavers of chafers in the webs, and the next year there were even more spiderwebs and dead bodies.”
But the spiders alone weren’t responsible. They were receiving a helping hand from another introduced species—rabbits. About 99 per cent of all redback webs are constructed inside abandoned rabbit burrows, and research by University of Otago zoology students Stacey Bryan and Jackie Spencer found that Cromwell chafers were the second-most-common prey item strung up in their webs. One “super spider”, says Spencer, had killed 70 beetles.
The rabbits had to go. But the reserve is in a difficult place for eradication: it verges on the township of Cromwell and is a popular spot for dog-walkers, meaning that poison, shooting and fumigation are out of the question.
Instead, DOC turned to Wanaka man Billy Barton for help. Barton uses his own unlikely alliance to eradicate rabbits: dogs and ferrets.
When Barton and I arrive at the Cromwell Chafer Beetle Nature Reserve, the remnants of the previous night’s stars are flecked across a faded sky. It’s a crisp winter morning and snow blankets the mountains.
Barton pulls his red truck into the paddock and unlatches the top half of the boot. Five dogs jostle to be the first one out. He’s dressed head-to-toe in khaki fleece, a beanie pulled over his greying mane, and he looks a bit like a friendly pirate—silver hoop earrings and smile-creased blue eyes.
The reserve is pockmarked with burrows and swollen with warren hummocks. The dogs gambol up to a burrow and their noses disappear into the hole. Barton follows, toting a cat carrier. Inside are his secret weapons: ferrets.
When we reach a burrow that the dogs deem promising, Barton lays nets of fluoro orange and yellow over each opening, securing them with tent pegs.
“From the rabbits’ perspective, they don’t see the net,” he explains. “Its colour means it is obscured by the bright light as they come up out of the burrow.”
Then, out come the two ferrets: white fur, red eyes glowing, a flash of sharp teeth. Barton captured them in the wild.
“I caught about 15 before I found three that would let me handle them,” he says. “That proved sore on the hands and fingers. They bit me a lot, but I persevered.”
He picks up one by the shoulders and then holds it by the front paws, swinging it gently back and forth.
“This is how you relax a ferret,” he says. “It seems to calm them down.”
I’m not sure what the difference is between a calm ferret and an agitated one. Barton tucks it into the burrow, under the netting. One of the dogs, Becca, is poised above the rabbit burrow, head cocked, directing her ear into the entrance, wet nose twitching. Muffled thumping emanates from beneath the ground and all eyes, human and canine, jerk in the direction of the vibrations.
Silence. Insects chirrup. Cars slip past on the main road, a hundred metres away.
With a sudden burst of action, the dogs are off, in a frenzied pursuit of an escaped rabbit. It bounds across the field in a wide arc. The two spaniels stretch out their necks, as if willing their short legs to carry them faster. Becca surges ahead, snatches the rabbit in her jaws and winds down to a slow lope.
Not all catches are so exciting. Usually the rabbit leaps into the tangle of netting and Barton dispatches it with a swift pull to the head.
His method wastes nothing. The rabbits are gutted on the spot, innards left for the local harriers, carcasses fed to his dog. The occasional batch of meat makes its way into one of his famous rabbit curries.
“Ferreting is safe and no harm can come to the public,” he says. “It’s a natural way of rabbit control.”
Keene says that compared to other methods, Barton’s has “less paperwork, less expense and an equally good result”.
Barton follows strict rules to keep his ferrets—they must be neutered, must wear tracking collars when hunting rabbits, cannot be returned to the wild, and cannot be displayed, in case anyone thinks they might make good pets.
“Ferreting requires a lot of patience and time to take a young ferret from the wild, provide it with suitable housing, put up with bites and keep handling it so it doesn’t bite you too often,” he says. “I don’t give them names, unless they bite me.”
But for Barton—and the chafer beetles—ferreting is worth it. This is his third season working at the reserve and so far, results are promising. In 2014, 460 redback spiders were found in Spencer’s surveys; in 2017, this had reduced to 123.
A poster proclaiming ‘Beetles are beautiful too’ adorns one wall of Barbara Barratt’s lab at Invermay in Mosgiel. Buckets filled with soil, vegetation and chafer beetles are lined up on a bench.
Barratt and her team are figuring out how to raise them in captivity. It’s a process that begins with DOC staff capturing adult beetles by night, soon after they emerge in early October.
“They only come out on warm spring evenings, but they’re pretty fussy about the conditions that they’re active in,” says Keene. “Even on nights that we think have the right conditions, it can be pretty hit-and-miss.
“They don’t run away when you walk up to them, so they’re quite easy to collect. You just pick ’em up and put ’em in a jar.”
When the adult beetles arrive at the lab, they’re paired up and sorted into buckets, which are left in the insectary, a glasshouse with one mesh wall to keep the temperature comparable to outside. They’re fed on broccoli, in addition to the vegetation in their home.
“Within two or three weeks, we’ve got eggs,” says Barratt.
One thing the larvae seem to thrive on: carrots. “Think we could plant the reserve out in carrots?” Barratt laughs.
Adults raised in captivity are released back into the wild, and Barratt aims to establish new sub-populations across the reserve.
Like the beetles they look after, the scientists and rangers working to save Cromwell chafers are understated. For decades, they’ve been quietly persisting in their efforts to learn as much as they can about this odd invertebrate, while interest from local communities has waned.
Meanwhile, the pressures of urban development are on the rise. Last year, a letter to the editor of the Otago Daily Times from a developer proclaimed the Cromwell Chafer Beetle Nature Reserve “prime land suitable for housing” and suggested the beetle population be translocated to a smaller site, further away, lest “a few dozen beetles get the blame for escalating an affordable housing crisis in Cromwell”.
The land is protected under the Reserves Act, so it’s not in imminent danger of being scabbed over with subdivisions. But this sort of thinking is a perennial problem for conservationists tasked with looking after less-charismatic species.
The Cromwell chafer beetle is what’s known as an umbrella species: through its protection, an extremely rare ecosystem of inland dunes and gravel beds is also being preserved. The beetles help to protect, by proxy, a range of dryland valley-floor plants, including the only known Central Otago site of the rare dwarf woodrush (Luzula celata), a creeping plant with silver-green tufts.
Large swathes of this type of dryland habitat have already succumbed to irrigation and land development, making the Cromwell Chafer Beetle Nature Reserve a place of great ecological importance.
“You can see how it’s difficult to get enthusiastic about a fairly nondescript brown beetle,” says Keene. “But on the other side of the coin—where does it all end? This habitat type is already incredibly rare.”
In some ways, the Cromwell chafer beetle is lucky. Its nocturnal habits and inland-dune home caught the attention of Charles Watt, and its proximity to an urban centre may be the reason it received formal protection.
Some of the beetle’s close relatives haven’t been quite as fortunate.
The Prodontria genus is endemic to southern New Zealand, comprising another 15 known species. One lives not far from Cromwell: Prodontria modesta is found only within a 10-kilometre radius of Alexandra and is thought to be threatened. Another species, undescribed and known only from a pasture near the township of Five Rivers on the Southland plains, may have already disappeared into the abyss of extinction. As for the others, we don’t know enough about them to ascertain whether they’re in trouble.
This lack of knowledge is typical for invertebrates, which remain woefully understudied in New Zealand. We know that around 500 of New Zealand’s invertebrate species need conservation research and we think that maybe another 500 do, too—but we know so little about them that we can’t be sure.
But there’s something about this little brown beetle that has helped it survive this far. Despite the transformation of its home turf and new pest species moving in, the beetle has persisted.
“It’s a unique part of New Zealand’s natural heritage,” says Keene. “Once it’s gone, it’s gone. I think it is always going to be range-restricted and naturally rare. But I like to think they should keep bumbling along in there.”
For the people working to save it, the next big challenge involves making sure others ascribe value to the land and the beetle, too.
“The reserve belongs to the people of New Zealand,” says Barratt. “We’ve got to try and make them feel proud of it.”