Partula Snail

Partula tohiveana

Partula Snail (Partula tohiveana): The Tree Snail Zoos Brought Home

Partula tohiveana, the Tohiea tree snail, is a small left-coiling tree snail from Moorea in French Polynesia. An introduced predatory snail wiped it out in the wild. Zoos kept it alive from just four individuals, and since 2016 zoo-bred snails have been released back on Moorea, where they now breed again.

Habitat

Upper valleys of Moorea's eastern ridge, on climbing pandanus (Freycinetia demissa) up to 4 m above ground

Size

Shell up to 13.7 mm long; left-coiling (sinistral)

Breeding

Gives birth to live young, about 16 a year; mature at 6-12 months

Range

Endemic to Moorea, French Polynesia; reintroduced to Afareaito valley

Conservation

Critically Endangered (IUCN 2025), downlisted from Extinct in the Wild

Main threats

Introduced rosy wolfsnail (Euglandina) and New Guinea flatworm

Habitat & range

The Tohiea tree snail lived only on Moorea, one of the Society Islands of French Polynesia. It was naturally restricted to the upper parts of the valleys along the island's eastern ridge, where it lived mainly on the 'ie'ie, or climbing pandanus *Freycinetia demissa*, up to about 4 m above the ground (Gerlach et al., *Oryx*, 2026). Partula snails are famous among biologists: the dozens of species that evolved in neighbouring valleys of Tahiti and Moorea have been studied for over a century as a textbook example of evolution on islands (ZSL).

Life in the trees

Partula snails live on leaves and stems rather than on the ground, and they feed by grazing on the thin layer of plant material, fungi and microbes on leaf surfaces (ZSL). The shell of *P. tohiveana* coils to the left (sinistral) and reaches a maximum length of 13.7 mm. Unlike most snails, Partula do not lay eggs. They are ovoviviparous, giving birth to fully formed young: *P. tohiveana* produces about 16 babies a year and is mature at 6 to 12 months old (Gerlach et al., *Oryx*, 2026). That slow breeding is one reason a fast predator could wipe them out.

Lost to the rosy wolfsnail

In the 1970s the predatory rosy wolfsnail (*Euglandina rosea*) was introduced to Tahiti and Moorea to control another invader, the giant African land snail. Instead it hunted the native Partula. Between 1982 and 1995 the wild partulid populations of the Society Islands were eliminated, and *P. tohiveana* was declared Extinct in the Wild (Gerlach et al., *Oryx*, 2026). A predator-proof reserve built on Moorea in 1995 failed. Today the introduced New Guinea flatworm *Platydemus manokwari* is the main predator.

Saved by zoos and sent home

Before the last wild snails disappeared, scientists collected survivors. *P. tohiveana* passed through a bottleneck of just four captive individuals (Gerlach et al., *Oryx*, 2026). An international breeding programme led by ZSL London Zoo, with partners including Detroit Zoo, Saint Louis Zoo, RZSS Edinburgh Zoo, Bristol, Marwell, Whipsnade and Woodland Park Zoo, kept Partula species alive in small leaf-lined boxes for decades (London Zoo, 2025). London Zoo keeper Dave Clarke saved the last nine snails of one species in 1991 (ZSL). Releases of *P. tohiveana* into the trees of Moorea's Afareaito valley began in 2015-2016. The first wild-born baby was found on 29 September 2016 and the first wild-born adult in 2018. By September 2024 a resident wild-born population was living there, making it the first Extinct in the Wild invertebrate to be re-established, and in 2025 the IUCN moved it to Critically Endangered (Gerlach et al., *Oryx*, 2026). Across the programme more than 17,000 Partula snails of several species have been returned to Tahiti and Moorea (ZSL); in September 2024 alone, about 6,000 snails of 10 taxa were released (Saint Louis Zoo).

Fun facts about Partula Snail

• Partula snails give birth to live, fully shelled babies instead of laying eggs.
• Every Tohiea tree snail alive today descends from just four captive snails.
• Released snails are marked with UV-reflective paint so researchers can find them at night with an ultraviolet torch, up to about 5 m up in the trees.
• The snail that wiped Partula out, the rosy wolfsnail, was brought in on purpose as biological pest control.
• P. tohiveana is the first invertebrate species to be re-established in the wild after being listed as Extinct in the Wild.

Partula Snail vs Common Bombardier Beetle

The Common Bombardier Beetle's quick chemical spray and predatory instincts give it the edge over the slow snail in a forest-floor meeting.

In the damp leaf litter of a tropical forest, a Partula snail inches along a low branch while a bombardier beetle patrols the ground below. Spotting the soft-bodied mollusk, the beetle climbs up and delivers a targeted spray of hot, irritating chemicals from its abdomen to discourage the snail from retreating into its shell. The snail pulls back at the first sting but cannot match the beetle's speed or agility. The beetle persists with short bursts until the snail's exposed foot is irritated enough that it loosens its grip. With the snail dislodged and vulnerable on the ground, the beetle claims the encounter, though both animals survive to move on another day.

Read more about Common Bombardier Beetle.

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