Local Focus: Mysterious giant snails found in Tōtara Reserve Regional Park

Horizons Regional Council is asking the public to keep an eye out for Powelliphanta marchanti snails which have recently been sighted at Tōtara Reserve Regional Park.

The "hearty carnivores" can apparently gobble earthworms like spaghetti and don't mind taking a dip in the ice-cold Pohangina River.

Biodiversity adviser Ruby Mountford-McAuley was pleased to hear of the snails' arrival.

"We don't have records of them being here previously, so it's why we're interested to know if anyone has any information about how they got here," she said. "They are really susceptible to predators. So it's really cool that we know they're here."

Powelliphanta marchanti are giants of the snail world, measuring up to 9cm across and displaying strong patterns and brightly coloured shells. But that doesn't mean they're easy to spot.

Previously, the closest known location of the snails was at the headwaters of the Pohangina River. Scientist Lorraine Cook is unsure how they might have travelled the vast distance to Tōtara Reserve, but it wasn't by foot.

"We think it's probably equally likely that they made their way here being washed down the Pohangina River," she said. "But there may have been a bit of human intervention and someone may have dropped them off here either thinking they had an empty shell or dropped off some live snails."

Shells of the native species were first spotted in 2017. Since then, Horizons Regional Council have received multiple reports of more shells, and even a live snail was found.

"We were able to get the snails identified by Dr Kath Walker, who is our go-to for snail expertise. So she was able to identify the snails in the shells that we found is Powelliphanta marchanti," Mountford-McAuley said.

Powelliphanta marchanti are among our most threatened invertebrates. Cook believes their immigration to Tōtara Reserve could be a reflection of the intensive pest control programme currently under way.

"There's two main things that threaten powelliphanta snails generally. One being predation by introduced mammals, and the other one being habitat modification and deterioration through fire and grazing, and browsing by introduced ungulates like deer and pigs.

"So the fact that they are here could reflect the fact that predator control is being done and perhaps deer population is low and the habitat is in a generally good quality."

Regional response officer Ray Palmer believes pest control will help the snails live their "best lives".

"We're trying to reduce the rat numbers in the reserve and to help the birds and their life, and the snails of course.

"The main predators being hedgehogs, rats and stoats. Also the occasional cat and ferret.

"Tōtara Reserve is one of the last remnants of native bush for the Manawatū area. We have 600 or more bait stations currently in the reserve and we've got 150 traps which we service once a month. It's a very intensive programme and we're hoping that we see some really good results."

Mountford-McAuley hopes for public assistance to solve the mystery of how these snails ended up in Tōtara Reserve.

"What we're hoping is that if any members of the public spot any of the snails, that they can let us know. They can send us photos and GPS coordinates," she said.

She is also hopeful that someone might remember their parents or grandparents dropping the shells off at Tōtara Reserve in years gone by.

"The more records we can get, the more we know," she said.

It is illegal to remove any live snail or the snail shells from the park as they are protected under the Wildlife Act, but you can report sightings to Horizons by phoning 0508 800 80.