Wednesday, 9 January 2008

Snails on the edge

Next week I'm heading back down to Portland in the far SW of the state to look for snails. (I was there on holiday a few weeks ago: here, here and here.) The plan — as long as the boss signs all the travel forms — is to map the distribution of the introduced white snail (Theba pisana).

Theba pisana occurs naturally along the Mediterranean coast. It has become established in all sorts of places around the world. In Australia, the species thrives in the summer dry/winter wet climate of in the south of the continent. (Well, the summer dry/winter dry as it seems to be now.) And by thrive, I mean the snails turn up in their thousands.

So abundant is Theba in some places that it damages cereal crops. Not by eating them but by contaminating the harvest.

The snails climb vertical surfaces — fence posts, tree trunks, wheat stems — and seal onto them with a layer of mucus. They don't do much harm to the fences and tree trunks. Nor to the wheat, really. But when the harvester rumbles through, the machinery minces them up. By (did I mention it before?) the thousand.

Snail paté.

If there are no fences, trees or cultivated grasses, the snails climb up the next best thing. On the cliff tops at Portland, the next best thing is cushion bush (Leucophyta) — the bad-hair day xerophyte that lives on the windswept dunes.

But Theba isn't the only snail living on the edge. A native species, Austrosuccinea (on the right in the photo) takes advantage of the humid microclimate beneath the Leucophyta. Very little is known about this succineid. So there's another project to get stuck into … but not just yet because they're mostly found on controlled land, so I'll need a permit. And that takes time.


Anonymous said...

Snail ... it is so good to read of you heading out to do some real work ... important work ... :)

Among my earliest memories are being out in the paddock after the header, standing on my own box, so I could reach to sew wheat bags up.

budak said...

more bizarre snails!

Snail said...

I guess even that part is mechanised now, jj. And probably for the best!

Gary Barker's done a load of work on agricultural ecology and biological control of Theba but there doesn't seem to be any detailed info on distribution. Dots on maps --- it's fun!

Thanks for that link, B. Those Malaysian Opisthostoma are weird critters. I don't think we subscribe to Biol. Lett., so I'll see if I can get a reprint from one of the authors.

Snail said...

Geoff Baker not Gary Barker. D'oh!

budak said...

you can download the paper here!


While you are at it, also try to come up with a better explanation of why these snails & their relatives like to climb so much. That is, better than the commonly offered reason that they are trying to move away from the hot ground, which I don't quite believe is the case.

Snail said...

Can't think of an alternative explanation but all the snails we saw were on vertical surfaces, even though they might not have been very far off the ground. They also seemed to be quite picky at some venues, favouring particular fence posts and not others.

That, in itself, might be an interesting little project. *Adds it to list of things to do*