Biologists uncovered the unusually large specimen of the spider's tree-dwelling genus Hadronyche while canvassing Booderee National Park.

The 50-millimetre female was burrowed inside a rotting log in a silk-lined nest up to two metres long.

Scientists estimate she is between 25 and 30 years old.

Further genetic and morphological analysis will be needed to determine whether it is a new species, but ANU biologist Dr Thomas Wallenius was pleased with the surprise find.

"It was unexpected that we'd find such a beautiful specimen," Dr Wallenius said.

"While a lot of the fauna is quite well documented, the surveys on invertebrates [in the national park] haven't been done as intensively so we're currently working to see if the funnel-webs fit into current classifications."

While the tree-dwelling funnel-web differs morphologically to its ground-dwelling Sydney cousin, Dr Wallenius said "both are quite dangerous".

It is hoped by learning more about the biodiversity of the funnel-web populations in Jervis Bay, researchers will be able to ensure accurate identification and administration of antivenom in case of a bite.

The first funnel-web antivenom was developed in 1981 after scientist Struan Sutherland heard of the death of a seven-year-old girl who was bitten by a funnel-web near Jervis Bay.

More than three decades on, scientists still have much to learn about Australia's most notorious spider.

The discovery is part of a wider biodiversity study of the area.