Slimy invaders from afar have long been a staple of science fiction, thrilling and chilling audiences. Slimy invaders as a fact of farming life are much less entertaining.

Every season, before he starts seeding, Yorke Peninsula farmer Graham Hayes has to lay snail bait.

If he doesn't do so, his crop will be destroyed by millions of Mediterranean snails.

"Well if they are in large enough numbers they'll just eat all of the crop," Mr Hayes said.

"There's nothing that we grow that we can avoid having troubles with snails ... if it grows, they'll eat it."

Those "troubles" occur right across the growing period.

In the early stages, while a crop is still green, Mr Hayes said the snails would eat it.

When the crop ripens, snails get caught up in harvesters: clogging the machinery and contaminating the grain.

CSIRO scientist Geoff Baker is Australia's foremost snail expert, having spent three decades musing over the molluscs.

He has warned this year has the potential to be a bumper snail season, for two main reasons — the recent wet and mild summer, and the snails' ability to juggle their breeding cycles.

"This is a bet-hedging strategy that the snails use, and many other invertebrate animals use, where they'll sit tight if the weather's not great for reproducing or they'll go gangbusters if it is great," Dr Baker said.

"And that, unfortunately, is what this season is looking like."

The snails arrived on Yorke Peninsula more than a century ago, as slippery stowaways aboard sailing ships coming to collect grain.

Dr Baker said there were four distinct species of snail.

Generically they are all called the Mediterranean snail because of where they originated.

"They have distributions all the way from Scotland down to Morocco from Portugal through to the Middle East," Dr Baker said.

"So there's a big, wide distribution, they've come accidentally to Australia and they've become a problem.

"They've hit pay dirt, they've escaped the natural enemies that have a huge impact on their abundance in their native habitat."

Snail problem stretches beyond Yorke Peninsula

Dr Baker said it was not just South Australia's Yorke Peninsula that had a snail problem.

"Right from near Geraldton around the coast all the way," Dr Baker said.

"Some are in Tasmania and up into southern New South Wales, but the pest problem with them, where they get into very high numbers is very much South West WA, and particularly the coastlines of South Australia and Western Victoria."

Snails on Graham Hayes' Yorke Peninsula farm. ( ABC News: Simon Royal )

The snails' economic impact is considerable.

They cost millions of dollars a year to control.

Baiting helps, as does running huge heavy rollers over the stubble to crush snails before re-seeding.

Mr Hayes was especially proud of a locally modified machine that sieves out small snails from canola crops.

There is also an emotional impact, something perhaps only another farmer can really appreciate.

"I had a phone call the other day from WA and this one chap said he'd been through bouts of depression because he thought he was the only person with snails in the district," Mr Hayes said.

"He talked for an hour on the phone and he was so thrilled to talk to me about how we deal with them and how we've had them for so long that it's not the end of the world. You can go on farming."

Snails quicker than most thought

Nevertheless, Yorke Peninsula Landcare adviser Michael Richards described the measures available as harm reduction, not elimination.

"We still haven't got the ability to break their lifecycle, we've got the knowledge and ability to handle them in the crop and reduce the contamination risk," Mr Richards said.

Yorke Peninsula farmer Michael Richards and Graham Hayes try to get rid of the growing number of snails. ( ABC News: Simon Royal )

The answers will come from science, and also snail-cam.

Three years ago, Mr Richards helped install a series of cameras on Mr Hayes' farm.

They've been revealing some unexpected secrets, such as a snail's pace is a faster more than anyone had thought.

"During summer where previously we thought they were shut down — the technical term is estivating — we've now got evidence of them moving in summer, thanks to the humidity overnight," Mr Richards said

"Traditional information was that snails would move 20 to 30 metres in a year was the sort of level of science, and we are seeing them move 8 meters in an evening with 5 to 7 millimetres of rain."

That sort of information has helped reshape those control measures, like baiting and rolling.

Spanish fly could be the key to snail woes

But Dr Baker believes the best hope is to find a natural predator: flies that lay their eggs on snails.

That's turned out to be easier said than done.

Dr Baker said one fly that showed real promise was refused entry into Australia because in lab testing it showed an interest in native snails.

Then, a few years ago, a fly from western France was given approval for release.

Dr Baker said that fly has proved a bit of a disappointment because, in something of an irony, Australia's snails are not French.

"Although they look the same, they are the order of species difference," Dr Baker said.

"The actual origins of the snails now look to be in Morocco, Southern Spain and Southern Portugal and that's where we should have been importing our parasites from the in first place ... that's how specific the relationship is."

According to Dr Baker, a southern Spanish fly is now showing the best promise of controlling snails.

Final approval to release it, assuming it's granted, is still some time off, but Dr Baker expects to start the long and detailed permission process later this year.

Mr Hayes said the fly could not land soon enough.

"Oh wonderful, I can't wait to find a place to put them!"