WAYS OF THE WILD.

Auckland Star, Volume LXVII, Issue 253, 24 October 1936, Page 1 (Supplement)

WAYS OF THE WILD.

LAND SNAIL PLACOSTYLUS.

SPECIES NEARING EXTINCTION

(By A. W. B. POWELL.)

«One of the most interesting representatives of our native land fauna is fast nearing extinction. Only a snail certainly, but an aristocratic one, and one with commendable habits at that. The snail, known to science as Plaeostylus hongii, and to the Maori people as pupuliarakeke (literally, flax snail) has a striking shell up to three inches in height by an inch in width, solid in structure and coloured rich chestnut-brown with the aperture reddish. There are three species of Plaeostylus known from New Zealand and all three are restricted to north of Auckland. One was confined to the Big King, Three Kings Islands, but is now apparently extinct, another is found only at the extreme end of the northern peninsula, and the third once extended from Whangaroa to Whangarei Heads. These snails are vegetarians, feeding on dead karaka and pohutukawa leaves. They are decidedly coastal in distribution, always preferring the pohutukawa covered slopes and cliffs. If we trace the present distribution of all the relatives of the pupuliarakeke (Plaeostylus) we find that outside New Zealand waters related species occur only in the Melanesian Islands, northwards to the Solomons and eastward as far as Fiji. This vast area of distribution of these snails coincides exactly with the now submerged "Melanesian Plateau," a complex system of connecting land which, at a moderate depth, unites with the North Auckland Peninsula all the Melanesian Islands in which these snails occur. Deep water in the Tasman Sea separates this former continent from present Australia-, where no snails of this type occur. Largest Species Already Extinct. It is these inferences behind the study of the mere snail that makes this study a work of such absorbing interest, and it would indeed be a calamity if these living pieces of evidence of New Zealand's continental past were allowed to become extinct. Unfortunately our largest species Plaeostylus bollonsi, from the Three Kings Islands, has already met with this' fate. This fine snail, which is over four inches in length, was first discovered in 1901 by the late Captain J. Bollons. Fifty specimens only are known to have been taken, and now this species seems definitely to be extinct. The tragic extinction of the species was probably brought about as follows:— When the Aupouri Maoris fled from the northern mainland they settled at the Big King, evidently cleared much of the island for cultivations, and thus diminished the snails to a very small colony, which did not manage to increase to any extent after the Maoris left and the island again became forested. The introduction and subsequent spread of goats has now cleaned out most of the undergrowth, rendering conditions no longer suitable for these large snails. The second species of Plaeostylus ambagiosus, which once occurred in teeming millions all round the coastline of the extreme north, has had its numbers so reduced that it also will become extinct unless something is done to preserve as sanctuaries the small areas occupied by the two surviving colonies. One of these colonies is on the small Cape Maria Van Diemen Island, and the other is in a small area of original forest at Unuwhau, between Spirits Bay and Tom Bowling Bay. Disappearance Factors. It was here that I found the first nests of Plaeostylus; they were cylindrical depressions in the soil of about one inch in depth, and the same in width. The eggs, which hatch by heat generated by the decaying leaf mould, numbered from 15 to 18 per nest, were thinshelled, oval, and about a quarter of an inch in length. A very disconcerting feature was the fact that most of the eggs had been eaten out by ants, and probably only about two or three out of each batch ever reach maturity. The lack of insectivorous birds in the district is probably the cause of this. At Cape Maria Van Diemen Island a few of these snails still exist on The steep faces, living arotmd the roots of flax, but the colony has dwindled considerably in recent years. Although separated from the mainland by only a few hundred yards of water, the Cape Maria snails differ slightly from the mainland ones, and suggest the development of a new species by isolation. It would indeed be a, matter for regret if this interesting evolution of a fourth Plaeostylus should be brought to a sudden close by the extermination of the

species. Millions of the bleached shells of Placostylus still litter the coastal dunes of the Far North, grim evidence of the changes wrought by man with his fires and indirectly through the introduction of pigs and rats, both of which take a heavy toll of the snails. The remaining species of New Zealand Placostylus is more fortunately situated, and under present conditions is likely to survive indefinitely. Although it has almost entirely disappeared from the mainland between Whangaroa and Whangarei Heads where it formerly existed in large numbers the species still flourishes at the Poor Knights Islands, 10 miles off the coast from Whangarnru. A Gratifying Exception. On the northern island of the Poor Knights Placostylus is so abundant that one encounters them strewn among the leaf mould practically everywhere from the sea cliffs to the highest peaks. However, on the southern island of the group these snails are very rare owing to the long residence there of wild pigs. Fortunately the pigs were exterminated a month or more ago by a party under Captain G. F. Yerex, of the Department of Internal Affairs. Captain Yerex found one or two living snails on the southern island, so there is now hope that with the removal of their chief enemy, the snails may increase again. In order to emphasise the devastation caused by pigs, I mention two visits made to a delightful bush-clad headland near Mimiwhangata, first in November, 1027, and later in January, 1035. On the first occasion Placostylus was found to be abundant over the entire headland, each tuft of native grass having around its base a cluster of snails of all ages. Some years later a herd of domestic pigs from a nearby- farm over-ran the place and hardly a snail escaped destruction. On my second visit the ground was strewn with hundreds of the eiuriehed shells of the members of >• former flourishing colony. It was at this spot that I found the only lefthand coiled Placostylus so far known. These snails are easily kept in captivity, for a few dead karaka leaves are all they require for food.