Flax snails (pūpūharakeke)
Flax snails belong to the genus Placostylus, and were known to Māori as pūpūharakeke. Three native species are recognised. They live in coastal broadleaf forests and surrounding scrubland in northern New Zealand.
The genus is distributed in the South Pacific, with different species in New Caledonia, the Solomon Islands, Fiji and Lord Howe Island. It is not certain whether these species trace their ancestry to Gondwana, or arrived in New Zealand more recently.
The tall, spired shell of the largest flax snails can reach up to 8 centimetres in length. The young live in trees and feed on micro-organisms that grow on the leaves. When they mature, they move down to the ground. Despite their name they do not feed on flax, but eat the fallen leaves of trees such as karaka, kohekohe and rangiora.
A different Placostylus species lives in the forests of New Caledonia, where locals regard it as a delicacy. In New Zealand, there is some archaeological evidence that Placostylus were once eaten, but today neither Māori nor Pākehā have any enthusiasm for eating snails .
The largest and most visually striking New Zealand snails are members of the family Rhytidae.
The large kauri snail (Paryphanta busbyi, known to Māori as pūpūrangi), is found in northern New Zealand. Although it occurs in kauri forest regions, it does not live close to kauri trees, as the nearby ground is probably too dry for the worms on which the snail feeds. It also eats insects and snails, and may live more than 20 years. The shell is a dark, greenish-brown flattened spiral, up to 10 centimetres in diameter.
Super size snail
Powelliphanta snails are giants of the New Zealand snail world. The largest species, Powelliphanta superba, can grow to about 10 centimetres across (about the size of a hamburger), and weigh up to 90 grams – as heavy as a mobile phone.
The closely related genus Powelliphanta is widespread in the wetter parts of central New Zealand, especially north-west Nelson and the West Coast of the South Island. At least 21 species have been recognised, in habitats ranging from temperate rainforest near sea level to mountains near the bushline. Some have beautifully coloured and patterned shells.
Powelliphanta are carnivores, eating worms (which they slurp like spaghetti) and slugs. They are mainly nocturnal, living in leaf mould or under logs, and only appearing at night to forage.
Powelliphanta snails lay up to 10 eggs a year. Each egg is 12–14 millimetres long, with a hard pink shell like a tiny bird’s egg.
Mollusc scientist Baden Powell made detailed studies of New Zealand’s largest snails, then included in the genus Paryphanta, in the 1930s. When some of the snails were moved into a separate genus, it was named Powelliphanta in his honour.
There are about 30 species of native New Zealand slugs. All have a characteristic leaf-vein pattern on their upper side, for camouflage. Māori knew them as putoko ropiropi. Their biology is poorly known, but they are thought to live mainly on algae and fungi on the surface of plants. Slugs may huddle together, apparently to create a humid microclimate. They may also cluster around small pools of water or wet humus on larger leaves.
Native leaf-veined slugs have only one pair of tentacles – unlike introduced species, which have two. Also, the native species do not damage garden plants.