Flax snail  (Placostylus hongii)

Classified as Vulnerable (VU) on the IUCN Red List 2007 (1).

Endemic to New Zealand, flax snails (Placostylus spp.) belong to the world’s oldest land snail family, which originated 200 to 300 million years ago (3). The long, coiled brown shell of this large snail species can reach enormous lengths of more than eight centimetres (2) (4). Some populations contain albinos, which are characterised by a white to pale-yellow rather than bright orange or red colour within the shell opening (aperture). The outside of the shell (periostracum) is also paler brown in some albinos, but the shells of the two forms otherwise appear identical (5).

This flax snail is recorded from New Zealand’s mainland at sites between Whangaroa and Whangarei on the Northland coast, and from the Poor Knights, Chicken, Mokohinau and Great Barrier Islands offshore. However, a number of populations are now extinct or believed to be extinct (6). Recently translocated populations are also present on Motuhoropapa (6) and Matakohe/Limestone Islands (7).

Flax snails generally inhabit coastal broadleaf forest and scrub, residing in pockets of leaf-litter on the ground (2) (4). Young flax snails live on the leaves in the tree canopy, only coming to live on the ground when they have grown sufficiently large (4) (8).

These nocturnal snails hide in the leaf litter during the day and come out at night to feed on fallen leaves (4).

Mating appears to be triggered by rainfall and probably occurs every year, except in periods of drought. These snails may mate several times with several different partners. Egg-laying has been observed between November and February on Poor Knights, when 20 to 30 eggs are laid in a shallow nest in loose earth. Nests containing 30 or more eggs are thought to be the result of more than one snail laying in the same nest (8). While adults tend to stay in and around a relatively small area, juveniles disperse (9). These flax snails reach maturity at three to five years of age and may live to over 20 years (8).

Like other large flax snails, this species has been badly affected by mammalian predators introduced to New Zealand, such as rodents, pigs, hedgehogs and possums (8). Habitat destruction and modification wrought by human settlers and the domestic and feral animals they brought, such as sheep, cattle, horses, goats and pigs, which graze, browse and trample vegetation, has also had a dramatic and devastating impact on flax snail numbers (2) (8). These threats continue to grow and, without intervention, could lead to the extinction of one of New Zealand’s largest native snails (8).

Management of the main flax snail colonies has existed since the early 1980s, mostly through poisoning rodents, enhancement planting, fencing colonies, and stock control (2). Two of the main colonies (Whangaruru North and Peach Cove) are also protected within scenic reserves (8). Wild populations have been translocated to Motuhoropapa Island and, following a successful captive-breeding programme, 11 captive-bred individuals were released onto Matakohe/Limestone Island in August 2002, each snail attached with a harmonic radar transponder to help follow its progress (9). A year later, nine of the original snails were found alive, along with a newly hatched juvenile, indicating that the snails had bred successfully (7). New Zealand’s Department of Conservation created a Giant Land Snail Recovery Plan in 1995, which has since been updated, and aims to prevent extinction and focus management towards the most genetically diverse populations (2).

View information on this species at the UNEP World Conservation Monitoring Centre.

For more information on flax snails and their conservation see:

• Parrish, R., Sherley, G. and Aviss, M. (1995) Giant Land Snail Recovery Plan Placostylu spp., Paryphanta sp. – Threatened Species Recovery Plan Series No. 13. Department of Conservation, Threatened Species Unit, Wellington, New Zealand. Available at:
  www.doc.govt.nz/upload/documents/science-and-technical/TSRP13.pdf