Finding a red-eyed fairy cicada is like finding a needle in a haystack, but for the first time in four years one has been sighted.

The tiny cicada is the size of a 5-cent piece and was recently spotted on a creek bed in Nowra on the NSW south coast.

Cicada expert Nathan Emery has been examining the cicada and said he was surprised to find it so far south.

"We had a few specimens found in 2013 and 2014," Dr Emery said.

"This was up at Eloura and the Blue Mountains, so we thought the distribution was more Sydney-based.

"All of a sudden, a keen naturalist in Nowra posted a few photos and I thought, 'Hang on a second, I think I know what that is'."

Cicada named after Dr Emery's sister

The original two red-eyed fairy cicadas found by Samantha Emery in 2005. ( Supplied: David Emery )

Dr Emery has a long-standing connection with this particular species of cicada, because while he cannot take credit for its discovery, he was there when his sister Samantha found it.

He was cicada-hunting with his sister and father in the Royal National Park south of Sydney in 2005 when they came across the tiny species.

"Sam was quite frustrated, it wasn't quite going her way that day," Dr Emery said.

"She looked down onto a spinifex plant and saw these two little green cicadas.

"She took a sweep of her net and got them both at once and it turned out to be a new species."

The scientific name for the cicada, Samaecicada Subolivacae, was named after Samantha.

Cicada life a mystery

While little is known about the species, Dr Emery thinks it follows the standard life cycle of a cicada, but because they are so small it would likely be accelerated.

Typically a cicada will lay eggs on a tree. Once the eggs hatch, the larvae drops to the ground and burrows under to feed on tree roots.

Cicadas spend most of their lives underground, staying there for up to seven years.

Once they emerge, they find a mate and die within one to four weeks.

Dr Emery is a cicada expert and science officer with the Australian Botanic Garden in Sydney. ( Supplied: Nathan Emery )

"The smaller cicadas like this might come out annually or just every couple of years," Dr Emery said.

He said the conditions that encouraged them to emerge were unknown, and because the species was so small it was hard to know whether it had always existed in the landscape and only recently been uncovered, or whether it had migrated down.

"The distribution could have changed because of urban spread," Dr Emery said.

"When you lose tall trees, you lose the cicadas. The smaller it is, the harder it is to find."

Dr Emery will now use this sighting to increase the known distribution and study the specimen.

He is also encouraging people to take part in the great cicada blitz to help identify other rare species.

Visit inaturalist.org for more information on how you can take part.