Powelliphanta snail

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Population: Unknown
Threat status:
Varies between species
Found in:
Native forests, especially around north–west Nelson and north Westland.
Did you know:
These species of native carnivorous snails are the largest in the world, some growing as big as a man’s fist. They suck up earthworms like spaghetti but are among our most threatened invertebrates. Rats and possums are major predators.

Powelliphanta snail is at risk from a predator plague caused by high levels of seed production ('beech mast') in 2014. Battle for our Birds protects Powelliphanta snail and other native species from predators.

Facts

Hidden away in New Zealand’s forests and grasslands is a bewildering array of native land snails, which range from the microscopic to the massive.

Among these are at least 21 species and 51 sub-species of Powelliphanta or Mount Augustus snails – which represent some of the most distinctive invertebrates in New Zealand.

Powelliphanta lignaria johnstoni, Charming Creek, West Coast. Photo: Jess Reedy.
Powelliphanta lignaria johnstoni, Charming Creek, West Coast

Powelliphanta snails are not your common garden snail! In fact, they are totally unlike garden snails, which are a European import and an unwanted garden pest.

Powelliphanta are giants of the snail world. They can reach up to 90mm across, or the size of a man’s fist.

They are also beautiful. Their oversize shells come in an array of colours and patterns, ranging from hues of red and brown to yellow and black.

And Powelliphanta snails are most unlikely to be found in your garden. Most favour living in the forest, and particularly like to eat earthworms, sucking them up through their mouth just like we eat spaghetti!

In fact, these meat-eating giants of the forest floor are true biological oddities. They are as representative of New Zealand’s unique evolutionary history as the kakapo, moa or kiwi.

Unfortunately, they are also one of the most threatened of New Zealand’s invertebrates. A total of 40 species or subspecies are ranked as being of national conservation concern.

Quick facts

  • Powelliphanta snails are carnivores. Their favourite prey is earthworms, but they are also known to eat slugs.
  • The largest species is Powelliphanta superba prouseorum, found in Kahurangi National Park and measuring about 90mm across. These are the sumo wrestlers of the snail world, weighing in at 90g, or the equivalent of a female tui!
  • The genus was named after Dr A.W.B. Powell, a former scientist at Auckland Museum who studied the snails during the 1930s and 1940s.
  • Powelliphanta snails used to be known as Paryphanta snails, until the 1970s. Now, Paryphanta refers only to kauri snails, which live north of Auckland.
  • Powelliphanta snails are hermaphrodites, meaning they possess both male and female reproductive organs and therefore can mate with any other adult Powelliphanta.
  • Powelliphanta snails lay about 5-10 large eggs a year. Each egg is up to 12-14mm long, pearly pink and hard-shelled - just like a small bird’s egg!
  • Powelliphanta are nocturnal. For the most part, they live buried in leaf mould or under logs, only coming out at night to forage and to mate.
  • It is estimated that Powelliphanta snails can live up to 20 years. In snail terms, that is an incredibly long life span!
  • Because Powelliphanta snails are prone to dehydration, they cannot survive in dry conditions. For this reason, they are more common in moist high-altitude forest than in drier forests at lower altitudes.

Rare white snail discovery

The fascinating find of a rare white-bodied giant Powelliphanta snail was made in the Flora Stream area of Kahurangi National Park in November 2011. The white snail is a brown-based Powelliphanta hochstetteri hochstetteri that had its characteristic golden brown-spiralled shell but with a body that was a glowing white rather than the usual deep black colour.

Powelliphanta hochstetteri hochstetteri (white morph). Photo: Maria Brooks.
Rare albino Powelliphanta snail

Snail distribution map.
Snail distribution map

Albinism is known to occur in many animal species around the world. The absence in pigment, which could be partial or complete, was due to a genetically-inherited defect in the enzyme which produced melanin.

Department of Conservation Powelliphanta expert Kath Walker said it was exceptional to come across an albino snail. From the photos it looked to be an adult snail at least 10 years old. It is amazing it survived so long as its white body would make it clearly stand out to be picked off by weka or other predators.

Where to find Powelliphanta

The stronghold for Powelliphanta snails is in north west Nelson and north Westland, where most of the species occur.

They are also found in the Marlborough Sounds and Mt Richmond Forest Park, as far south as Fiordland and Southland and, across Cook Strait, on parts of the Kapiti Coast and into the central North Island.

Different Powelliphanta species can be found from sea level, where they live in rich temperate rainforest, to above the bushline. Most of the alpine species have to contend with prolonged snowfalls and bitterly cold winters. The most likely sign of their presence will be empty snail shells on the forest floor.

Visitors will be unlikely to spot a live snail, except at night or occasionally on rainy days. They are most likely to be active on warm, moist nights after a long dry spell, when they will be out foraging for food.

Story about snails

Meet snail man David Roscoe - Conservation Blog 29 June 2012

Threats 

Kath Walker with hundreds of snails which have been predated by rats and possums. Photo: Martin De Ruyter/Courtesy of Nelson Mail.
Kath Walker with hundreds of snails which have been predated by rats and possums

Despite being legally protected, New Zealand’s Powelliphanta land snails are under serious threat. Several species are in danger of extinction, particularly from predation and habitat loss.

The main predators are possums, pigs and rats, although weka, thrushes and hedgehogs also eat them. Possums only recently developed a taste for the snails, and appear to be incorporating them into their diet over increasing areas.

As a result of major habitat loss in the past, many Powelliphanta populations are now restricted to tiny pockets of native bush, where they have a precarious toehold on existence.

These isolated populations can be threatened further if the bush is removed, opened up by stock trampling or dried out by drainage of nearby paddocks, as the snails need moist conditions to survive.

1080 poison helps native snails

Possums cause massive problems for New Zealand's native species.

This video explains how periodic use of the biodegradable poison 1080 to kill possums has reversed the decline in snail populations.

Video by Trakabat

DOC's work 

Powelliphanta hochstetteri obscura. Photo: Rod Morris.
Powelliphanta hochstetteri obscura

The Department of Conservation undertakes a number of programmes to protect Powelliphanta populations.

Possum control, particularly in the upper South Island, aims to protect several species.

On Mt Burnett, in Golden Bay, DOC staff could only find about four live Powelliphanta gilliesi gilliesi snails in every hundred square metres in 1994. By 2003, following two aerial possum control programmes, searchers were finding almost 14 live snails in every 100 square metres.

On Mt Arthur, in Kahurangi National Park, searchers could only find about three Powelliphanta hochstetteri hochstetteri snails in each of three sampling plots in 1993. By 2003, after a decade of annual ground control of possums, about 15 snails were being found in each plot. At the same time, in a nearby site where no possum control takes place, less than three snails per plot were being found.

Powelliphanta hochstetteri hochstetteri.
Powelliphanta hochstetteri hochstetteri

Rat control, combined with weed control, revegetation and wetland restoration, is helping to secure a future for the Powelliphanta traversi koputaroa snail near Levin.

Recently, there has been a dramatic drop-off in the number of snail shells being found attacked by rats. In the past, DOC staff found caches of predated snail shells throughout the area, but this is not occurring anymore.

One species, Powelliphanta gilliesi brunnea, is slithering towards recovery in Golden Bay, thanks to a combination of habitat protection and predator control measures. Restricted to half a hectare of farmland, DOC has erected an outer fence to exclude farm stock, an inner fence to exclude rodents and hedgehogs, and has planted native trees to increase the habitat available. By 2003, there were about 1000 individual snails present, compared to about 350-500 in 2001.

You can help

Powelliphanta lignaria lusca shell. Photo: K.Walker.
Powelliphanta lignaria lusca shell

The Powelliphanta snails found today are the culmination of at least 80 million years of evolution on New Zealand’s isolated landmass, developing a set of peculiar characteristics that is totally unique in the world.

They represent a small but significant part of our natural heritage which deserves to be saved.

  • Support possum and rodent control programmes in your area. These have proven to be safe and effective ways of protecting Powelliphanta populations in New Zealand.
  • Don’t take empty shells from snail habitat areas. These are formed from calcium in the environment, so it is important that the calcium is returned back to the environment for other snails to use in the future.
 

Find out more

Learn more

Contacts

DOC's 24 hour emergency hotline:

0800 DOC HOT (0800 362 468)

Call to report sick or injured wildlife, and whale or dolphin strandings.