Wellington has its very own snail species, Potamopyrgus oppidanus, found nowhere else in the world – and it’s smaller than a grain of rice. But their numbers are alarmingly decreasing due to bikers and weeds.
Science Researcher Lara Shepherd tells us where they are found and what we can do to help save this rare species.
Te Ahumairangi Hill
Most people in Wellington appreciate the town belt for providing a scenic backdrop to the city and opportunities for recreation and connecting with nature.
But not everyone realises that the town belt is also important as habitat for native species. For example, the freshwater snail, Potamopyrgus oppidanus, is only known from Te Ahumairangi Hill (formerly known as Tinakori Hill), less than 1km from the Beehive.
Where is it found?
This small snail, which is only 3mm long, is found in damp gullies and seepages with bush cover and undisturbed leaf litter.
It was first described in 2008 by Dr Martin Haase and the type specimen (the specimen on which the name is based) is held by Te Papa.
Potamopyrgus oppidanus was classified as Nationally Critical in 2018, the most threatened ranking available.
However, it’s now in even more trouble. Bronwen Shepherd (Te Ahumairangi Hill Ecological Restoration) and Dr Karin Mahlfeld (Wellington Open Science Lab) recently surveyed the snail population and found it is now rare in areas where it was common a few years ago.
The most significant threats to the snail come from the construction of illegal mountain bike tracks on the hillside.
Track building is harmful to snails because it removes vegetation cover and leaf litter, increasing run-off and sediment.
Weeds such as wandering willy, which smother snail habitat, can also be spread by track building.
What can you do to help this unique snail?
If you live in Wellington you could attend a planting working bee to restore the damaged forest on Te Ahumairangi Hill.
If you’re a mountain biker then only ride on authorized mountain bike tracks (there are four such tracks on Te Ahumairangi Hill).
There is a valuable lesson to be learned from Potamopyrgus oppidanus – even small patches of indigenous vegetation can be home to unique plants and animals. It is therefore important to conserve as much of this diversity as possible, even in the middle of our capital city.