​ Getting the numbers on giant snails

The number of giant land snails in the Nelson backcountry is thought to be declining due to predators and habitat disturbance but there is a lack of data to confirm their status.

Nelson Nature is working with the Department of Conservation to rectify this, by setting up permanent snail monitoring locations at several sites along the Bryant Range. These will be used to estimate snail density and detect any decline, or a possible comeback if effective predator control is established in the future.

Our local giant snail species Powelliphanta hochstetteri consobrina is only found in the Richmond and Bryant ranges behind Nelson. It is threatened by introduced predators such as possums, rats and pigs, as well as habitat disturbance by goats, deer and people. A recent snail count at the sites found low numbers, indicating that predators are taking a heavy toll on the population.

Sharp-eyed trampers may have occasionally noticed the impressive shells as they walk the tracks in these areas. Despite the full-grown shells being about 60mm across, live snails are rarely seen as they are uncommon, nocturnal and well camouflaged. If you do find empty shells on your travels, please don’t take them home as they are fully protected by the Wildlife Act and are used by other snails as a source of calcium.

Giant snails are a great indicator species for the health of an ecosystem as the conditions they need to thrive (deep, moist leaf litter and very low predator pressure) are the same conditions that support a healthy forest.