Mol­lusk mys­tery solved


They are small in statue but their sud­den ap­pear­ance raised some big ques­tions which have fi­nally be an­swered.

Blen­heim man David Ol­liver was left puz­zled by thou­sands of empty snail shells which ap­peared on his path and drive­way ev­ery time it rained.

The ec­cen­tric grass snails ( Val­lo­nia ex­cen­trica) were dis­cov­ered lay­ing empty and crunched un­der­foot ev­ery time David and his wife, Pat, left their house.

Now an aca­demic from the Mu­seum of New Zealand Te Papa Ton­garewa has re­vealed the snail shells were washed there by the rain and wind. Col­lec­tion man­ager sciences and mala­col­o­gist Dr Bruce Mar­shall says the snails are found in huge num­bers.

‘‘ Val­lo­nia ex­cen­trica live in pas­tures and can oc­cur at high den­si­ties of up to 1500 per square me­tre.

‘‘It lives for only a few months, and has two gen­er­a­tions per year.

‘‘As a con­se­quence there may be large num­bers of empty shells in a small area of grass. The empty shells on the path pre­sum­ably floated there from the ad­ja­cent grass.’’

Val­lo­nia ex­cen­trica is a species of very small air-breath­ing land snail which was in­tro­duced to New Zealand from the Mediter­ranean and Western Europe.

They grow to be­tween 1.2 and 2.3 mil­lime­tres in size and are dif­fi­cult to see with the naked eye.

David says he only found the snails af­ter hear­ing the noise the empty shells made when they were walked on.

‘‘It’s mar­vel­lous to fi­nally have some an­swers,’’ he said.

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