The snail's burden

September 19, 2009
Their admirers reckon they should be the flagship native animal for Nelson, but others may struggle to see what the appeal of a large, meat-eating snail really is. Geoff Collett looks at the plight of the powelliphanta. --------------------
A CARTOON appears unexpectedly near the start of the otherwise dry and technical "recovery plan" that Conservation Department scientist Kath Walker has written for New Zealand's entirely bizarre and widely under-appreciated giant land snail. It shows a streetwise panda offering some world-weary advice to an innocent snail: "You wanna conservation group? You gotta learn to be cute."
Bad news for snails, in other words, even for ones as unusual and eye-catching as the various species that live deep in the hills around northwest Nelson - a place unrivalled in the world for the presence of large, colourful, meat-eating snails.
They may be fascinating and flat- out strange; they may be a direct link to the ancient origins of this country; several of their various species may be seriously endangered - but even the most ardent snail-o-phile would have to balk at calling them "cute".
The Nelson-based field officer for Forest & Bird, Debs Martin, an avowed fan of the creatures, recalls how, when some kakapo chicks were put on display at Nelson's Brook-Waimarama sanctuary last year, people flocked in their thousands to get a look. You don't, she muses, see many people lining up to see giant snails.
Even their name could be seen to be against them - nobody has come up with anything better than the apparently unpronounceable "powelliphanta" bit of their scientific label. (It comes from a Mr Powell; try saying it po-well-i-fanta; otherwise, just think large- carnivorous-land-snail).
If the snails have a champion, it is surely Kath Walker, based in Nelson because of its proximity to snail country, and DOC resident expert on the creatures.
Part of her ongoing fascination with them, she admits, is that, for all she knows of them, there are fundamental things about their ways that nobody understands. But right now, she just wishes snails could get a better press, some more respect for what they are, rather than the attention always being on the occasional controversies they get ensnared in.
The news media, she says, only take an interest on those occasions - most famously when the entire population of one particular species was discovered on land destined for coalmining on the West Coast. The snails were uprooted and moved to make way for the diggers, but not before a long-winded and expensive scrap between state coalminer Solid Energy and various environmental groups. The environmentalists continue to snipe, saying that evidence of the snails dying off in their new homes is evidence the relocation has been a failure.
The snails have appeared more recently in the argument over Meridian Energy's plan to dam the Coast's Mokihinui River; in the debate over letting mountainbikers into parts of the Kahurangi National Park, including the Heaphy Track, and whether cyclists could endanger them; and in one of DOC's most bitterly-argued activities, its use of 1080 pesticide to kill possums in tracts of the Kahurangi. While it may not be universally recognised, the use of the controversial poison in the park is first and foremost being done for the benefit of the snails.
Ms Walker is cautious about getting caught up in such controversies, but can't hide her exasperation. "I'd love to make it so we rejoiced in them more, " she says.
Her enthusiasm isn't as infectious as she might hope it could be. The information guides she has written on powelliphanta occupy a small, quiet corner of the DOC website and straightforward information on them is hard to find.
She holds on to a near-20-year-old New Zealand Geographic magazine that devoted a few pages of a lengthy article on snails to powelliphanta; in terms of non-contentious mainstream coverage, that's largely it. The Solid Energy saga may have confused matters. For one thing, difficulties in estimating the snail population on Mt Augustus before the miners moved in meant DOC and Solid Energy grossly under-estimated how many snails would be found. They expected some hundreds and found more than 6000, provoking sneered criticisms that the snails could hardly have been endangered after all. Other critics liked to calculate out the per- snail cost, given claims that the relocations had cost $10 million.
Perhaps the most colourful evidence that snails were at least temporarily seen by the wider world as a totem species for "greenies" came from a much-quoted line by then Tasman mayor John Hurley, who denounced "radical-green fishing fanatics and bird-counting, snail-watching freaks".
Then there were the hints of disapproval from some quarters when it was discovered that, by powelliphanta standards, the Mt Augustus variety was quite small - their shells growing to perhaps 4cm wide, less than half the size of the giant snails found in parts of Golden Bay.
Ms Walker says, ruefully, that sympathy for the snails might have been greater if they had just been that much bigger.
Debs Martin similarly laments the experience of the Mt Augustus campaign, which Forest & Bird was central to. "That was what we were meeting - a lot of misinformation about the snails and also just a general lack of enthusiasm for them . . . they're not bright birds and they don't have a gorgeous song; they haven't got lovely feathers or anything like that."
Such is the pecking order of conservation, it seems: bigger is better; bright and fluffy beats slow and slimy every time. You gotta be cute.
It's not all bleak, though. The Mt Augustus saga at least raised the snails' profiles and Solid Energy has been keen to promote its efforts in relocating the Powelliphanta augusta (as the coalmine species came to be known) with a DVD, Snail - the Movie.
DOC's possum-control work in the Kahurangi has led to resurgent populations there and a much better chance of trampers encountering live snails. The department says its aerial 1080 operations in Nelson-Tasman have the primary purpose of protecting specific snail species (although with benefits for other species, too), and in parts of Golden Bay/Kahurangi National Park, the resurgence in snail populations has been remarkable. Parts of the Heaphy and Flora tracks are littered with live snails when the conditions are right - usually in damp weather after a dry spell. "You can walk along the Mt Arthur Track and if you're in the right conditions, you have to watch your feet, " Ms Martin says.
The fact that possums have been destroying some snail populations is a relatively recent discovery, Ms Walker says. It has principally been a problem where other food sources are sparse.
The snails have other enemies, too. Their principal natural predator is the weka and introduced species have acquired a taste, especially thrushes, pigs and rats, which will patiently gnaw their way around and through a shell over an extended period. The survey work suggests that possums, though, have been the No 1 killer.
The mystery surrounding the snails has always been much of their appeal; as recently as 1995, an entirely new species was discovered at a tiny location in Golden Bay.
The great unknown is their intense selectiveness about where they will make their home. True, some species are scattered reasonably widely through Kahurangi National Park, but others exist within a tiny area, somewhere they have called home, as far as humans know, for millions of years.
In some places, Ms Walker says, you can see why; in others, it is almost inexplicable. The Mt Augustus snails are a classic example, concentrated around the tops of a remote, frigid, rain-soaked, foggy mountaintop, and nowhere else in the world. As Ms Martin puts it, there are "populations that are separated and never cross, even though they're within tens of kilometres of each other".
The reason why is the fascination for Ms Walker. "That's actually why I'm still interested in them . . . it's that intriguingness."
The scientist in her refuses to speculate on what could be at play. Still, the presence of so many specific populations, splintering into dozens of distinct species and subspecies, suggests - as one Massey University scientist told a journalist a couple of years ago - "Darwin's entire thesis being displayed for us in New Zealand".
That powelliphanta are concentrated in northwest Nelson and north Westland may reflect, Ms Walker says, that the high country they call home was a refuge during ancient inundations and was spared glaciation, and that it today provides a wet, warmish environment. Particular populations have set down in particular places, maybe bounded by river or mountaintop, stayed there, and evolved into something distinctively different from other powelliphanta. Different size, different-shaped shells, different colours, different patterns. Along the Heaphy Track alone, Ms Walker counts at least six distinct species or sub-species.
While powelliphanta can be found across a long geographic spread of the country - in selected spots down much of the West Coast, and north to Mt Taranaki - nowhere else has the northwest corner of the South Island's density or variety, and the Heaphy, she says, is "snail city".
She struggles to think of another creature with such a deep connection to this part of the world. So does Ms Martin, who suggests, with tongue only partly in cheek, that "wouldn't it be great if we had a flag that had snails waving on it as everyone entered the top of the south region".
That is probably being too ambitious for this slow-moving, little-understood creature with some mildly dubious characteristics. Still, hope springs eternal in the breast of the powelli- phile. "A while ago, during this [Mt Augustus] campaign, I was given a sweatshirt that someone handpainted for me: 'Save Our Snails, SOS', " Ms Martin says. "I wear it often and I'm surprised by the number of people who recognise what I'm talking about now . . . I'd love to see more people with a Save Our Snails sweatshirt on."


Some things you may not know - or may not have wanted to know - about powelliphanta snails
They lay a hard-shelled egg through a hole in the side of their neck. The egg has a hard, limey shell like a small bird's egg. In lowland species, they take 2-6 months to hatch. In higher altitudes above the bushline, the eggs can take 12-14 months. As well as being slow-moving, they are slow-growing, only reaching breeding age at five or six years, and potentially living 15 years, which is tending to the ancient in invertebrate terms. Again, at higher altitudes, they may be even slower-growing. While they are carnivorous, it's really only earthworms who have much to fear from becoming a powelliphanta feast. They prey on different-sized worms, the bigger species targeting large, native earthworms. They hunt the worms out and grip them with rows of inward-pointing teeth; the worm, meanwhile, uses backward facing spurs
 along its sides to try to hold itself in its burrow. If the snail wins this tug of war, the worm is dragged into the snail's shell, where the digestive juices get to work. For any gastronomes contemplating whether a powelliphanta would make a tasty feed for humans, in the tradition of the Frenchman's escargot, New Zealand Geographic has come up with the definitive answer: Don't go there. "It's been tried and found really revolting, " the magazine said in a 1990 report. Empty powelliphanta shells are a common sight around the Kahurangi National Park. The shells often have striking helix spirals and distinctive patterns; but alive, they are far more impressive, with the shells tending to a glossy sheen. They are also heavy - the largest species, Powelliphanta superba prouseorum, can weigh the same as a tui, about 90g. Scientist Kath Walker says there are about 12 distinct species of powelliphanta, but many break into 5-10 subspecies with their own distinct features - a legacy of how the different populations have spread and settled in distinct locations down the eons. While they might not be a flagship species for New Zealand conservation - or even for Nelson's own natural order - they do have a strategic, if subtle, presence in helping welcome new arrivals to the region. The spiral- shaped things in the carpet at Nelson Airport are said to represent land snails. --------------------