The arachnid has been named Megaspider and the park says she is roughly twice the size of a typical funnel web spider, more comparable to a tarantula.

The 8cm funnel web spider's 2cm fangs will be milked for venom that can be turned into antivenom.

The Australian Reptile Park on the NSW central coast is the only funnel web spider venom milking facility in the country and the antivenom produced there saves up to 300 lives a year, the park says.

Australian Reptile Park education officer Michael Tate has "never seen a funnel web spider this big".

"She is unusually large and if we can get the public to hand in more spiders like her, it will only result in more lives being saved due to the huge amount of venom they can produce," he said.

The park encourages citizen scientists to safely catch funnel web spiders to donate to the antivenom program.

The Megaspider was donated in a clear plastic container with no marking to say where it came from, and the park is now seeking its donor to find out where it came from in the hope of finding similarly large spiders.

Spiders can be donated to the park itself, as well as at a number of drop off points around Sydney, the Central Coast and Newcastle.

Australian Associated Press