New Zealand farmers Dean and Marjorie Blythen are poised for an unlikely spot in the history books — early next year their property, about 30 miles north of Auckland, will become home to the country’s first officially imported dung beetles.
In what will be the start of a nationwide rollout of the industrious little insects, Blythen expects his 200 Hereford cattle and between 500 and 600 sheep to be joined by perhaps 1,000 to 2,000 beetles at an initial release site on the farm.
Those beetles, among 11 species being imported from South Africa, Australia, France, and Spain, are currently in quarantine before an outdoor mass rearing program and release into the wild. The intentional introduction of an invasive species — sometimes dubbed an “exotic” when the result is benign — has generated some furor in a land where past invasives have trampled on native species.
Hugh Gourlay, senior researcher with Landcare Research, the environmental management company handling the beetles’ transition, says the species have been carefully selected to be the most active and effective in New Zealand conditions.
They have been matched to the variable climate, seasonal changes, temperatures and soils, and include a mix of day and night foragers. “The idea is that we’ll have dung beetles working 24/7 all round the year,” Gourlay says.
Which is just as well, as they have a mighty task ahead of them: cleaning up the poop left behind by New Zealand’s roughly 10 million beef and dairy cattle, themselves an introduced animal.
Gourlay says at any one time an estimated 5 percent of productive land — nearly two million acres — is not being grazed because it is soured by dung, which discourages cattle from feeding nearby.
In addition, he says, as these Frisbee-shaped piles of excrement begin to deteriorate they can contaminate waterways, provide a breeding ground for bacteria and flies, and contribute to global warming by emitting nitrous oxide.
While some dung beetles roll animal manure into balls and then bury it, the New Zealand varieties tunnel. They will live under the cow pats, pushing the dung down into tunnels where beetle grubs will feed off the nutrient-rich contents.
Gourlay says the beetles can remove a pile of cow manure in as little as 24 to 48 hours, burying it anywhere between four and 20 inches underground.
Beyond the broad environmental benefits, Blythen likes what he calls the health spin-offs. “If they bury the dung, in the process they should take the eggs of internal parasites down below their ability to hatch and come back to the surface again.”
The beetles also offer farmers another tangible bonus: saving money on fertilizer by protecting grass quality, aerating the pasture, and using the nutrients and nitrogen stored in dung to enrich the soil.
The overall economic benefits are hard to quantify, but a 2006 study published by the American Institute of Biological Sciences concluded that dung beetles were worth about $380 million annually to U.S. cattle farmers.
The introduction of any new species is always a touchy subject in New Zealand. Its native wildlife has suffered terribly as a result of the innocent — though in retrospect often reckless — import of unsuitable animals since European settlement in the first half of the 19th century.
For example, in the early days of the then-British colony, rabbits were happily ushered ashore, only to repay the hospitality by breeding profusely, stripping vast areas of pasture and undermining farmland with their burrows.
In a bid to control the rabbits, stoats, ferrets, weasels and even domestic cats were released into the wild, setting free a scourge of nature’s most efficient killers in an environment containing some of nature’s most defenseless wildlife.
More recent accidental imports, like the Argentine ant, now advancing steadily down the country’s North Island, and the German wasp, illustrate the disproportionally negative impact that even small insects can have.
The Environmental Risk Management Authority, the government agency controlling the introduction of new animals, plants and other organisms, gave dung beetles the go-ahead only after more than two years of investigation, reports, and public submissions.
As might be expected with New Zealand’s sobering track record, the proposal sparked lively debate and some controversy.
Submissions to the authority raised questions about possible conflict with the country’s 15 species of native dung beetle, which evolved at a time when New Zealand was covered in forest and still feed primarily on leaf litter.
Concern was also expressed about interaction with earthworms. Others objectors believed the beetles might spread animal diseases and some questioned their effectiveness in reducing parasitic reinfection rates.
Opposition to the introduction was partially muted by reference to the beetles’ benign impact in their native countries and the experience of Australia, which has imported more than 40 species since 1968.
Having neighboring Australia acting almost like a laboratory has been very helpful, says Andrew Barber, manager for the Dung Beetle Release Strategy Group, which represents farmers and other industry stakeholders. “We’ve ridden a little bit on their coattails,” he admits.
Meanwhile, Gourlay concedes that some of the issues raised by objectors cannot be answered without “20 years of intensive research” but on all the evidence available he remains confident and optimistic.
“We’ve struggled to find downsides,” he says, pointing to what he sees as the positive experiences of Australia, Hawaii and the U. S. mainland. “They all have had really good experiences and great results from introducing dung beetles.”
Still, some critics remain unconvinced and are left wondering if New Zealanders will look back in 20, 50 or 100 years and add dung beetles to the list of pests they should have seen coming.