Friday, June 5, 2015

Southland's largest land snail

Clockwise from top left: a very large species from Northwest Nelson, my late deceased Pupurangi, a Garden snail for scale, Travers’ snail from the Tararuas and the Guide badge featuring Travers.

Southland’s largest native land snail is the rare Fiordland landsnail Powelliphanta spedeni which gets to 3.2 centimetres, barely larger than the introduced garden snail.  Some native slugs exceed 6cm beating the snail into first place for the record as the largest native land mollusc in Southland.  They are protected from collectors, both by residing in the national park and being on the threatened species register.  This doesn’t stop them being predated by rats, pigs and possums and their future in the wild is uncertain.  They survive in captivity in the right habitat but need specialised conditions to breed.

I visited a school recently to talk about the Social Studies Fair which is being held in Invercargill in late June.  One of the boys said his project was on the Pupurangi or Kauri snail Powelliphanta busbyi.  I told him he was talking to the only person in the world who had kept one as a pet, this being of course before they were protected.  They are one of our largest landsnails reaching about 8cm across but that doesn’t stop them being the most boring pet in the world.  No amount of training would persuade the thing to jump through a flaming hoop.

 I lived in Auckland for five years while at secondary school and explored a lot of the Waitakere Ranges in that time.  We occasionally came across the snail shells – it was then called Paryphanta.  The expert on them was AWB Powell, the malacologist or conchologist if you like, at Auckland Museum.  I met him a few times and took him shells to identify.  He was particularly keen on landsnails, the largest of which were the two groups, Paryphanta and the Flax snails – Placostylus.  AWB was born on the day of the relief of Mafeking in the Boer War so not surprisingly the B in his initials is Baden, after Baden Powell, the hero of the siege.  It was the ideas developed during the siege and earlier in the campaign that Powell later turned into a small book Aids to Scouting, of which I have a copy.  In the front it says ‘The corrected proofs of this book accompanied the last despatches that got through the Boer lines’.  The book was a hit with English boys and soon afterwards was rewritten as Scouting for Boys, and thus the Boy Scout movement began.

Empty shells from near Green Lake

Back to the shells.  Powell was a copious collector and it has been unkindly suggested that he collected some of the rare forms and subspecies of Placostylus to extinction.  In a revision of the Paryphanta snails they were renamed Powelliphanta in his honour.  There are about 20 species and about 50 subspecies, vermivorous critters – that means they eat worms.  The large number of subspecies is the result of the separation of populations in Westland by rivers, slips and glaciers.  Isolated populations form distinct features after many thousands of years and become subspecies.  Powelliphantas get to 9cm across, the largest being the Superb snail.  I have seen them only occasionally – a few in northern Westland, in the Waitakeres and I’ve seen Travers’ snail  Powelliphanta traversi on the Pahiatua Track which goes through bush near Palmerston North.  Travers the snail was the icon of the Guide Jamboree held at Levin, a rare example of a mollusc being elevated to sainthood.  Hang on – what about the Bluff Oyster Festival?

Visiting the Waitakeres one day after heavy rain I found a Powelliphanta busbyi in a roadside ditch, near Huia if I remember.  I took it home and kept is alive for about a year living in a wire-netting topped wooden box in our fernery.  I put in worms but never saw it eating them.  Eventually, when there had been no sign of activity for a few weeks, I discovered the shell to be empty.