Giant snails the winners

Date:  26 October 2010

Last weekend the final stage of an aerial 1080 pest control operation was completed over 3430ha in the NW Ruahine Forest Park, the primary aim being to protect giant snails from possum attack.

New Zealand has several species of giant carnivorous land snails which are only found in this country.  Powelliphanta marchanti, also known as Marchant’s snail, is found only in the North Island, with the Ruahine Ranges being one of the last strongholds. About the size of a match box, the shells are a browny-gold colour with a reddish-brown tinge in the centre. They are generally found above 900m and usually live 12-14 years but can get up to 20 years old.

Marchant’s snail, unusually spotted out
in the open on the main Ruahine Range

Being hermaphrodites, Marchant’s snails can either self-fertilise or store sperm for long periods, laying hard-shelled eggs during spring. During the day they keep moist under large logs in moss, leaf litter, or under skirts of tall tussock in alpine areas, coming out at night to seek out worms, which are their main food source. In the Ruahine Ranges they spend long periods under snow and remarkably are able to withstand below-freezing temperatures.

The Ruahine Corner area is considered a hotspot for biodiversity as it retains remnant populations of a wide range of other native species including kiwi, whio, kaka, North Island robin, NZ falcon, and kakariki. Lesser known are the rare plant species including beech mistletoe, dactylanthus and Pittosporum turnerei.

“All these species and the ecosystem as a whole will benefit from this pest control operation,” said Department of Conservation Area Manager Jason Roxburgh. “This is the third 1080 operation since 1994 and we have seen significant improvements, especially when compared to areas nearby that have not had pest control”.

Possums are opportunistic feeders of snails, meaning they have to learn to eat them from observing others possums. They leave a distinctive mark on the shells as they remove the snail, and these are recorded during monitoring.

“While possums are the primary target, stoats and rat populations will be significantly reduced in the short term,” said Mr Roxburgh. “This will give birds a reprieve from attack for the current breeding season at least”.

The current pest control operation is complemented by work carried out by volunteers in the same area. Known as Te Potae Project, it includes about 50kms of stoat trap lines across both public and private land. Volunteers are getting a break from checking the traps for a few months at least.

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