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Carnivorous snails
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Carnivorous (Rhytididae) snails of Otago
Did you know that Otago has 2 species of medium- and large-sized carnivorous land snails?
Carnivorous lands snails in the Southern Hemisphere belong to the family Rhytididae and are found in parts of the southwestern Pacific, Australia, southern Africa, and Aotearoa New Zealand.
A family is a taxonomic rank used in the biological classification of living and extinct organisms.
Taxonomy, in a broad sense the science of classification, but more strictly the classification of living and extinct organisms—i.e., biological classification. This is by arranging organisms into natural, related groups based on some common factor related to each.
In Aotearoa New Zealand there are several different kinds of carnivorous snail, including the large and rare Powelliphanta snails that eats earthworms. Smaller species like the Rhytida eat an array of animals, such as arthopods.
Carnivorous snails can move surprisingly fast to grab prey with its mouth. Once the prey is enveloped and suffocated, the worm is torn apart by the snail’s sharp, rasping teeth. These teeth, known as radulae, sit in a deadly ribbon in the snail's mouth.
All land snails have radulae, not just the carnivores. For example, the common garden snail has over 14,000 teeth, which it uses to eat plants. Other snails, which are detritivores, use their radulae to break down decaying plant matter.
Many carnivorous snails are threatened in Aotearoa New Zealand
A report from 2024 documents how a total of 109 taxa of medium to large land snails in the family Rhytididae had their conservation status assessed using the New Zealand Threat Classification System criteria. In total, 74 snails were assessed as being Threatened, 22 as At Risk, 5 as Not Threatened and 8 as Data Deficient (i.e. insufficient information was available to assess their conservation status).
If many of our land snails are to survive in Aotearoa New Zealand, the report highlighted the urgent need for action to control exotic browsers and predators, protect habitat and address climate change. In terms of climate change, it’s because drier soils make it hard for such land snails and their eggs to survive; they are reliant on moist conditions year-round. The warming climate has also allowed rats to expand into mountainous snail habitat which previously was free of rats due to the cold.
Don't take or move shells
Leave snail shells where they are. It's against the law to take or hold shells of some carnivorous snails, including Powelliphanta shells, or shells from reserves, without a permit.
Many live snails have been accidentally taken from their home and later left in a place where they cannot survive. It can be difficult to determine if a shell is empty.
In Otago we have two species of carnivorous snails: Powelliphanta spedeni spedeni and Rhytida otagoensis.
This species’ range includes parts of Southland and southern Otago, with a highly patchy distribution at mid-to-high altitudes, being found in tussock and beech forest. It grows to about 45 mm and has a fairly-uniform dark-green shell, but may have darker axial streaks, and can appear near-black when the shell is wet.
Powelliphanta spedeni spedeni has a national conservation status of Threatened – Nationally Vulnerable.
Powelliphanta spedeni. Photo: Samuel Purdie (CC-BY-NC 4.0) iNaturalist
Powelliphanta spedeni spedeni. Photo: Nigel Milius (CC-BY-NC 4.0) iNaturalist
Powelliphanta spedeni spedeni. Photo: Lloyd Esler (CC-BY-NC 4.0) iNaturalist
This species’ range includes throughout southern parts Otago and into Southland, occurring in lowland forest to moderately high-altitude tussock land. It is uncommon throughout most of its very patchy distribution, and likely extinct in places (e.g., Kaitangata), but still common in some spots. It grows to just over 20 mm, and has a very thin light-brown shell.
Rhytida otagoensis has a national conservation status of At Risk – Declining.
Rhytida otagoensis. Photo: Shou Saito (CC BY-NC) iNaturalist
In Otago we have 2 species of carnivorous snails in the family Rhytididae. A species list for carnivorous snails in Otago can be downloaded below.
To find out more about some of our carnivorous snails (Rhytididae) in Aotearoa New Zealand, visit the Te Papa Atawhai website to learn about Powelliphanta snails and the New Zealand Mollusca website.
Te Papa Atawhai | DOC
This website provides an overview of Powelliphanta snails, among the largest snails in the world and only found in Aotearoa New Zealand.
Mollusca.co.nz
This website focuses primarily on Molluscan species found with the New Zealand Economic Zone, including Rhytididae species.
