A population of the rare and unusual Nelson cave spider, which lives in the ‘Crazy Paving Cave’ in the Ōparara Valley on the South Island’s West Coast, is increasing and scientists think it is because the spiders have had a break from visitors.
With a leg span of 13cm and a 3cm long body, the Nelson cave spider/Spelungulae cavernicola is New Zealand’s largest native spider.
The spiders had been monitored for a number of years, with a steadily declining population, when the decision was made to close the cave to visitors in 2022.
Since then, spider numbers have shown a steady increase from an average of eight found during monitoring in 2022 to 33 in 2025. Rangers have also seen signs of the spiders breeding.
DOC Senior Ranger, Scott Freeman says people unknowingly interrupt the natural behaviour of the spiders with bright lights, vibration, sound, and the heat they bring into the cave.
“The cave has a low ceiling, and it’s quite small, so people get close to the spiders, which don’t like large creatures such as humans wandering round,” said Mr Freeman.
“We have proven in many parts of the country that when we remove or manage the threats, restore habitats or modify how we use or interact with nature, it comes back, and we can see that here with the spiders.”
It is thought that numbers of spiders may have peaked, and scientists are keen to see what happens in the next year before decisions about visitor access to the cave are made.
The spiders are relatively long-lived, with baby spiders taking two to three years to mature. Most spiders complete their life cycle in a year.
New Zealand’s native species are unique and special. On average, 70% of our nature is found nowhere else in the world. 93% of New Zealand’s estimated 2000 spider species are only found here.
Nelson cave spiders evolved separately from the rest of the world for millions of years and are thought to be directly descended from the earliest true spiders. They may be the missing link between primitive and modern spiders.
These spiders live near cave entrances and mostly eat cave wētā, which they drop onto while attached to the cave roof by their web. They are also found in Golden Bay and were the first spider species to be protected under the Wildlife Act.
The other walks and experiences in the Ōparara and the adjacent Box Canyon Cave remain open for visitors.
