West Coast cave closed to protect New Zealand's weirdest spider

New Zealand's largest spider - the Nelson cave spider grows up to 13 centimetres across. Egg sac, inset. Photo / Supplied

Squeamish readers be warned.

A popular West Coast cave is being closed for a year to protect a wonderfully gross resident - New Zealand's largest and most unusual spider.

The Nelson cave spider is known to live in the Crazy Paving Cave in the Ōparara Basin, Karamea. Measuring up to 13 centimetres across, it is the country's largest arachnid.

DoC has made the decision to close the Crazy Paving Cave for the next 12 months to protect them after a dip in breeding numbers.

The cave spiders size might be the most remarkable thing, but stranger still are where the spiders lay their eggs:

Young spiders are born in hanging egg sacs that swing from the cave roof. They look not unlike golf balls, suspended on thin stings of web.

Egg sac: The Nelson cave spider lays up to 50 eggs in the hanging pods. Photo / Supplied

DoC senior biodiversity ranger Scott Freeman says it is to protect these odd eggs that the Crazy Paving Cave will be closed, with immediate effect.

Although the number of spiders seen in the caves has increased since 2019, they have not been laying eggs.

"Only one egg sac has been seen since 2018," says Freeman.

"Breeding is the real long-term driver of the population so we want to close the cave to see if this will allow breeding to improve. Closing the cave means we can monitor the spider population's response to the removal of human visitors."

The Crazy Paving Cave - named for its broken stone floor - will be closed to visitors from June 1.

The crazy paving caves in the Oparara Basin. Photo / File

The nearby Box Canyon cave network will remain open and are free for visitors to explore in the Kahurangi National Park.

For more adventurous visitors, Ōparara's Honeycomb Hill caves contain 13km of passages with notable limestone formations but access is by guided tour only.

This can be booked through the Karamea Information Centre.

The Nelson cave spiders are found in small populations around cave entrances in Golden Bay and the Karamea Bight.

Protected under the New Zealand Wildlife Act, they are though to be the 'missing link' between modern and prehistoric spiders, from 350 million years ago.