Saturday, April 9, 2011

A Different Kettle of Snails

Did you know that there are some 2500 native snail species in Australia? And that none of them eat plants?
I spent a bit of time last weekend with the Toowoomba Field naturalists and Dr John Stanisic of the Queensland Museum, (who is Australia’s foremost expert on native snails), learning that everything I thought I knew about snails was very little and rather boring, compared to what there is to know.
The nub of it, though, was how important the natives are to the health of plants in our rainforests and brigalow scrubs.
They live on leaves, but don’t eat them. Instead, they eat the algae and fungi which grow in an almost invisible layer on the leaves, making a nuisance of themselves by blocking the plant’s pores.

The one in the photo above is a kind of snail called a semi-slug, which, as you can see, has just a rather miserable excuse for a shell. Semi-slugs live in rainforests, where the soil is low in calcium. Calcium is an essential ingredient in shells, so ditching the shell seems to be an obvious evolutionary response to scarcity of this basic ingredient.
Other native snails live in leaf litter and decomposing logs, where they are part of the all-important decomposition process that keeps the rainforests healthy.
We sometimes find these “snails” in our garden.
(Slugs, I learned , are regarded by snail specialists as just another kind of snail.)

Red triangle slugs live on the algae on trunks of trees and rocks - though I once heard of an enterprising person who introduced them to his bathroom, where they apparently kept the shower alcove clean. The red triangle on their backs marks the place which once, in evolutionary terms, a shell was attached. Note the “pneumostome” - the little breathing hole.
We also find these fellows in our garden. They are not natives, and are just one of the 60 or so species that have been introduced to Australia since white settlement.
I learned last weekend that they are edible, and known in the restaurant trade as “petit gris”. Now if we could all eat our pest snails (recipes tend to allow 12-20 per person for a meal), a major garden problem would be solved. What a pity I lack the courage. Have any of my readers tried them?
Native snails are rare in gardens, as they really need a healthy native ecosystem, full of microscopic algae, fungi, leaf litter, and so on, to survive.
It would be a gardening triumph to establish a garden which was able to support them, as does a carefully nurtured corner of the Boyce garden (corner Mackenzie and Range Streets Toowoomba). In the early part of last century, Dr and Mrs Boyce bought a block of land which contained a very heavily damaged rainforest remnant - the last existing remnant in suburban Toowoomba. They cared for the existing plants, carefully tended any natives which grew from existing seed in the soil, and did a little supplementary planting. Apparently the snails are an “indicator” of the health of an ecosystem, and the number and variety of snails now present in the Boyce garden tells us that it’s ecology is in good shape.

(These native snails were put on a leaf in the sun for the photo, and carefully returned to their damp and shady homes afterwards.)

Many modern gardeners are working hard on little patches of remnant land, clearing weeds, carefully protecting natural regrowth, and replanting local native species to restore the original environment. When they start finding native snails, they will know they have succeeded.

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