They grow to 1.5 metres in length but are hard to see — a deep underground squelching being the tell-tale sign for farmers of an elusive species on their property.

Key points: Giant Gippsland earthworms have a soft skin, so they need to live in permanent, moist burrow systems

Giant Gippsland earthworms have a soft skin, so they need to live in permanent, moist burrow systems The largest adult specimens measure up to 1.5 metres in length and are about the width of an adult thumb

The largest adult specimens measure up to 1.5 metres in length and are about the width of an adult thumb South Gippsland farmers report hearing gurgling sounds when the worms move through their tunnels close by

While you might not have heard of the giant Gippsland earthworm (Megascolides australis) until now, it's a threatened species that remains endemic to a small patch of eastern Victoria.

And a lot of work is being done to shore up its future, including local councils planning overlays to protect the worms.

Susan Taylor from the Department of Environment, Land, Water and Planning said authorities worked with landowners to ensure the worm's habitat was maintained.

"The giant Gippsland earthworm is a really interesting species in that it has been able to survive in these landscapes in which the native vegetation has been entirely removed," she said.

"It's a bit like a magpie … there are many species that once you remove their habitat, they disappear, but the giant Gippsland earthworm is still surviving under farmland.

"It's still surviving in areas that have been completely changed."

Digging the worms out of the ground usually results in their death. This image was taken when earthworks accidentally exposed them. ( Supplied: Beverley Van Praagh )

Ms Taylor said the worm was extraordinary, as the largest adult specimens had been measured up to 1.5 metres in length and about the same width as an adult thumb.

The worms have a soft skin, so they need to live in permanent, moist burrow systems — but the burrows are not filled with water as the worms need to breathe.

As a result, a gurgling noise can be heard above ground as the worms move underground.

"It sounds like water gurgling down a bathplug," Ms Taylor said.

Living with worms 'quite a privilege'

Libby Walters and Sam Gibson farm at Mountain View, between Warragul and Korumburra. Their 84-acre property is home to four colonies of giant Gippsland earthworms.

The worms live along a creek which feeds into the Lang Lang River.

"I feel like it's quite a privilege to have the giant Gippsland earthworm on our property," Ms Walters said.

Having cattle coexist alongside the worms was "pretty straightforward", she said.

"The cattle just graze the grass … they can't do much damage to the earthworms.

"However, we had been considering doing some revegetation work with Melbourne Water, and if we do that we have certain areas where the worms are and we have to be careful with how we space the trees there."

Libby Walters' property at Mountain View is home to a colony of the giant earthworms. ( ABC Gippsland: Peter Somerville )

Ms Walters said she had not seen nor heard the worms, as they never surfaced.

The colonies were identified by surveyors who visited the property.

"They found at least four to five colonies in wet areas fed by the springs," she said.

But the existence of the worm wasn't a surprise to her when she moved to the property in 2015.

"My grandfather was a mycologist and also had an interest in that sort of thing, so I'd heard about the worm many years ago through him.

"When the surveyors came out, they came with big sticks and walked around and would prod ... to stir up activity down there and then would stop, listen, and you'd hear a gurgling noise which is the worms moving through the earth."

As the worm moves through its tunnel, it makes a squelching noise. ( Supplied: Beverley Van Praagh )

Planning overlay offers protection

South Gippsland and Baw Baw councils have introduced planning scheme overlays that safeguard the worms' habitat against development.

Paul Stampton, acting director of development services at South Gippsland Shire Council, said the overlay did not restrict people in towns, although "it's quite likely the worms existed in towns in the past".

"It's really around farmland and where people build buildings," he said.

"The worm is vulnerable to deep ripping and hydrology changes, so the overlay really triggers if somebody is trying to build a large shed or something like that.

"It doesn't completely restrict it, but might say a survey has to be done and there are experts on the giant Gippsland earthworm who we'd get in and they'd say if the location is suitable or not."

Mr Stampton said a lot of the worms' habitat was on steep, south-facing slopes.

"So it's unlikely people would be building there, but if they do, they might be cutting into the soil to provide a flat pad for a shed.

"It's a very localised species between Korumburra, Loch and Warragul — because it's a very restricted habitat, it'd be great to look after that habitat as best we can."