tales of snails

Korero (AEWS), Volume 3, Issue 9, 4 June 1945, Page 6

tales of snails

A KORERO Report

New Zealand is a strange land with a strange fauna. The curious rarity of animals there is, of course, largely due to its being for ages cut off from the rest of the living world. When I began to discover the sunny forests and bush of the narrow North Auckland peninsula I found a side interest in chasing a rare and bonny snail quite restricted to a small region in this northern part of little New Zealand. Chasing ? Yes, amused pursuit of a slow snail ; one so large and interesting as to collect many names — bad ones. The Maoris call it pupuvangi, snail of the skies—l suppose because the shell is sky-blue inside, or because they found it up in trees. The shell is strikingly large for a land snail, the average about two and a half inches at its widest, two inches its narrow diameter, one and a quarter inches high ; but big ones can be nearly four inches. On hatching, the shells are nut brown. They are flat-topped and only grow green with age. The snails build their shells, grow them as a house for the body. Most snails can be removed from their shells. Fanciers used to transplant them from shell to shell, and each new inmate would add a bit of its own style to its new and different dwelling. So you could get artificially banded and patchycoloured shells. But a humble inmate of a slum dwelling forcibly put into a grand and beautiful home could only add slum walls. It’s hard to get the shell off without killing the proprietor, unless by carefully cutting away round the edges. You need to know what this snail’s enemy, a native woodhen, has learnt that, it’s

no good pecking the shell —it’s so hard and glassy surfaced. He wisely nibbles round the edges, pecking it gradually away. At last, there ! What a feast to the woodhen’s eye, to the human pecker what a view ! . . . the inside works working under the surface, the twochambered heart beating. But, alas, alive it is very difficult to find out anything about the snail at all, so sensitive is it to touch and whatnot. Laborious detailed anatomy is necessary, and gives drawings and microscope plates of beautiful, varied unsymmetrical forms and figures — nerves, vessels, organs, and geometric details of shell structure. Asked how you got all this from a mere snail, you can truthfully answer, “ I hacked him in pieces sma’.” I used to get into their out-of-the-way limestone and kauri forest world by bike or “ snailways ” —the Government system —and win a reputation among the “ backblock ” farmers for premature senile decay, wandering about in the bush on the hills in old clothes, crawling on my stomach after these so-called Gastropods or “ stomach footed ” things. Lonely farmers were obliging when they understood that you wanted to follow pigmy monsters and had to walk on your stomach nosing among moulds and roots. I met a very hospitable and sympathetic farmer, proud bearer of the name and blood of the famous eighteenth century French naturalist, Buffon. A. P. Herbert pities the snail crawling about on its “ tummy.” This underside is not really the tummy ; it and other inside works are up in the spiral part. It’s its foot. This snail’s foot is about 5 in. long, wide and leaf-like. Glands in

it produce a constant flow of mucous, a slime track on which its body and foot walks or undulates by muscular waves from back to front. An average snail’s speed may be funny. It’s not zero, but about one mile in sixteen days, fourteen hours—some one finds. Its soft foot lies always on a greased floor, protected from the rough ground. Though we cannot expect snails to leap off the ground, they can lift up their heads, and a few can burrow down a foot or two during droughts or winter. It is only in rare, abnormal cases that humans are hermaphroditic, whereas most snails are naturally. Each individual snail has the reproductive apparatus of both sexes, both sexes combined in one ; paring snails fertilize each other. Well, about the New Zealand snail. Snails lay eggs like birds, but this snail’s eggs are very large in proportion to the parent’s size. I’ve seen a snail from an isolated island off New Zealand, its one egg about the size of a thrush’s ; a specially adapted reproductive system, not for the mass production of marine snails, but for one superb individual product, like that of several tropical giants. The snail I’m describing lays very interesting eggs. I’ve collected them after much poring about, peeping under fallen clumps of parasitical treeplants, in well-protected, mouldy, damp, shady places as at the base of treetrunks or tall palms. I’ve never found them in the open, unprotected. Others have discovered them up trees among the dense grassy tree-plants I’ve just mentioned, like birds’ nests ; or like the Solomon Islands arboreal snails, and Philippine Islands species supposed to live near the tops of tropical forests. You may find as many as eighteen of these eggs neatly packed together ; they are white, oval, about a quarter-inch broad, hatching out fairly easily at ordinary temperatures, in moist conditions taking six weeks to two months. The wee snail comes out, not by the shell’s being pecked through, but perhaps by the mere process of expansion, all the time borrowing lime material from the egg-shell itself (which was originally borrowed from the limestone

habitat) and building it into its own baby shell. The egg-shell is weakened and can then be readily burst. Did you ever know such economical economists ? Now, it’s unparental and illegal, I know, but no parental care is exercised by either of the twin-sexed parents except that possibly moulds and similar food matter are chosen for the nest as food for the young. From ancient Tarquinium to Whipsnade snails have been farmed for epicures. My interest isn’t epicurean. This New Zealand snail is rare in being definitely carnivorous. You have only one or two carnivorous snails here, all the rest are confirmed vegetarians. I wish I could show you its teeth under the microscope ; they’d horrify you. Instead of molar teeth on a flat base, grinding leaves against a horny upper jaw, like most snails, this snail has real canine teeth, sharp pointed, backward-crooked cusps placed all round the mouth walls. Flesh is rubbed and scraped between two-toothed sides, not thirty or forty, but ten thousand. It takes a mass of muscles to work those rows of teeth. The common snail has about fifteen hundred herbivorous teeth ; the great black slug boasts thirty thousand canine teeth like our giant’s, and seems to be proportionally carnivorous and omnivorous. I’ve kept the giant snails among lettuce and leaves, but, hungry or not, they didn’t touch it. Most snails, being herbivorous, would be happy. So we see some snails have teeth like dogs and cats, others like cows—the great majority.

I didn’t believe in the “ whistling snail ” rumour from Ceylon and Hawaii. Still, I imagined that if I were an amplifier—or better an elf—l might hear some whistling, scraping,' whirring sound as one slowly gnashed and hashed and ground and tore to shreds its captured worm. Like the shell, a snail’s teeth are secreted throughout life. Perhaps twenty sets in a lifetime ! Shells can be repaired, even lost body parts can be regrown within limits. A temperature of 25 0 Centigrade kills the New Zealand one, 45 0 the common English snail ; the latter a much more adaptable creature altogether. Even a cold snail has a heart, a simple one with sluggish beat that stops almost completely during winter hibernation. But if heated up, any snail’s heart will beat quicker. Snails are photo-negative or light avoiding, and come out to feed at night, remaining hidden and inactive by day unless disturbed or livened up by rain. So I kept one or two of my carnivorous snails by my bed in glass jars, now and then getting up in the night to watch them, using a red light-shade, not to upset them. I kept them starved for a couple of weeks to ensure their being active. (No hardship when you know that some can live three or four years without food or water.) I saw them walking leisurely about the jars, into which I dropped a worm now and then. What then ? Slowly and deliberately they would protrude their

“ jaw ” or “ lips,” placing them over the worm, which made no violent struggle. The rows and rows of teeth grip it, and by a ratchet-like backward and forward motion slowly draw the worm in, protesting or unprotesting. I’d grab hold of the worm and pull gently, but the snail pulled as hard, and the prey couldn’t release itself or be released from those thousands of canine hooked teeth. If annoved, the snail would retract into its

shell with its rightful dinner. Now, one authority held that the remarkable leaf-like foot was a prehensile organ for capturing worms by crawling over them, holding them down in the foot holds till dead. But you could occasionally observe worms crawl of their own initiative into the snail’s big shell, while it was retracted and inactive. A few days later, faeces would be thrown out — no worm ! But you can’t trust every observation, though apparently snail had eaten worm while retracted.

Snails are muscular creatures. Trainers who turn them into horses can get them to pull up to fifty times their weight. So there might be a new unit of force—snail power.

The two pairs of sensitive tentacles are each regulated by a retractor muscle. Watch, and you’ll see how slow snails are to poke out their tentacles (probably by pumping them up with blood), how quick to withdraw them. The upper pair bear eyes, very short-sighted ones. But they move so slowly, young or old, they’re not likely to bump into anything. However primitive to us, each organ is well adapted to the needs of the total organism. Eyes which merely react to light, but tell them when pleasant night has come, when safe holes are reached. Scientists believe snails, like all lower

animals, are neither optimistic nor pessimistic, but entirely tropistic, their movements “ forced movements.” They don’t think. They just react instinctively to each stimulus as they must react. So when an experimenter gets a snail to improve its time for running a simple maze by as much as from two thousand seconds to two hundred, one ventures to believe it would require a host of such tests to half convince the scientist that a snail could either learn or think in any sense of those words. If you searched in the bush for those giant snails you might be disappointed seeing none about, till you lifted up a mass of palm fronds under a delicate palm tree. There ! Dozens of them. If only some god’s eye would let us see all that goes on in these sluggish grey-green life forms at home in this half-decayed pile fallen from the slender drooping palm grace above ; would tell us why dull eyes, deaf ears, three humble nerve ganglia, odour-sensing tentacles, should choose this particular blend of conditions. We can only see that darkness, coolness, dampness, shelter are essentials. The snails’ intimate reactions with each of these, with each other, and with the complex life of decaying matter are unknown. Some say snails will respond to a particular creaking on glass if the pitch is right. We all know how sensitive snails are to vibrations, also that, though seemingly blind and halt, nearer the inanimate than the live, they are guided by a trusty sense of smell. Nature draws no invidious comparisons between the snail’s superb sluggishness and the sparrow’s lightning turns. Though it can’t walk, run, or fly,

the snail group has colonized practically every environment from the abyss to the tree-tops and ten thousand feet up mountains. Desert drought is the greatest barrier to the land species. The New Zealand snail’s nearest relatives are in New Caledonia and Queensland. And this fact confirms the geologist’s map of New Zealand joined to New Caledonia some fifty million years ago when this genus first appeared. So snails are present indicators of ancient geography, just as they are sometimes good barometers. When in New Zealand in a dry summer you see those snails down at a stream side, in damp bush, and in a wet period in drier places, you see their bias towards humid conditions, their incomplete emancipation from their remotely ancient home, the sea, and from the vast majority of their snail relatives —still marine or fresh water. That giant snail, after all, like others, lives only four or five years. The snail group is hundreds of millions of years old.

Illustrations on pages 7,8, and 9 are three views of one pupurangi shell. The illustration at the top of page 8 is of a typical giant snail.