A miniature and rare species of crocodile is fighting back against a common Northern Territory pest by nibbling on the back legs of cane toads.

The dwarf crocodile was first discovered in Arnhem Land in the early 1980s.

It is also known as a pygmy crocodile due to its size and grows up to just a metre long.

Dr Britton's dwarf crocodile is six years old and still considered a juvenile. ( 105.7 ABC Darwin: Emilia Terzon )

There are thought to be only hundreds of the freshwater crocodiles across northern Australia.

In 2006, researchers were excited to confirm a new cluster of dwarf crocodiles near Bullo River, about 11 hours' drive south of Darwin.

After an infestation of cane toads moved into the river in 2008, there were grave concerns for the small crocodiles' survival.

The introduced American cane toad has toxic glands in its shoulders, eyes, ovaries and eggs.

Charles Darwin University crocodile researcher, Dr Adam Britton, said the notorious pest presented a "toxic prey" for the rare reptiles.

"If these crocodiles...grab [the cane toads] in their mouths and bite down into their toxin glands, they get enough toxin to kill them," he said.

Dwarf crocodiles adapt

One year after the cane toads arrived, Dr Britton and his partner recorded a 75 per cent drop in the Bullo River crocodile population.

"We were worried that they were completely going to disappear," Dr Britton said.

Yet they were also intrigued to discover the bodies of some unusually dismembered toads near the river.

"[My partner] found a large number of toads with twisted back legs and they had little teeth marks on them," he said.

There are no toxins in the hind legs of cane toads, meaning this part of its body is able to be consumed.

The nibbled cane toad bodies were therefore a hopeful sign that the dwarf crocodiles were figuring out how to safely eat their prey.

"If any crocodile actually seizes a toad by its back legs and successfully rips them off and eats them, it's going to learn that it can get a meal without being poisoned.

"They were learning and adapting to this toxic prey."

Dwarf crocodiles were first discovered at Bullo River in 2006. ( Supplied: Dr Adam Britton )

Last month, the team once again surveyed the area and found more dead cane toads with either whole or partial missing back legs.

They also found dwarf crocodiles in areas from which they had previously disappeared, adding weight to the team's cane toad adaptation theory.

"It's pretty conclusive that's what is going on," Dr Britton said.

Dr Britton and his partner are hoping to return to Bullo River next year to survey the region's more inaccessible areas by helicopter.

He said learning more about the elusive dwarf crocodile would help highlight broader issues with the environment and the impact of cane toads.

"It takes a lot to kill a crocodile but if their numbers decline you know that something serious is going on."