The remarkable recovery of the giant, fluorescent pink slug on Mount Kaputar has been tracked with the help of enthusiastic citizen scientists.

This striking slug, growing up to 20 cm long—longer than an average human hand—and 6 cm wide, exists nowhere else in the world except on the slopes of an extinct volcano in New South Wales’ Mount Kaputar National Park.

In 2019, devastating bushfires swept through the alpine area, wiping out an estimated 90% of the slug population. Yet, in 2020, around 60 survivors were spotted, offering hope for the species’ resilience.

Since then, the NSW National Parks and Wildlife Service (NPWS) has launched the Slug Sleuth app, allowing park visitors to report sightings, typically after rainfall on cool, misty mornings. To date, around 850 reports have been logged, with some observations noting dozens of slugs at once.

Through the app, people upload photos along with details of when and where they found the slugs. This data helps experts study habitat preferences and monitor the impacts of climate change on the population.

Adam Fawcett, NPWS threatened species project officer, had planned to conduct the first-ever formal slug survey just before the fires hit. Despite the setback, he remains optimistic, noting that the slugs are adapted to fire-prone landscapes.

“That fire was pretty bad,” he said. “We ended up with a large area of the summit burnt. Some areas were saved; some had had hazard reduction burns.

“But even though that fire ripped through there, really hot, the slugs came out after good rain in good numbers.

“We saw a mass breeding event, and because of La Niña the breeding continued.”

Thanks to the app, Fawcett and his team have been able to track the species’ recovery and identify population trends over time.

“In two sites, we’ve been getting about 200-odd slugs every time,” he sid.

“I get really excited, I go crazy taking pictures… I love when you see them doing something different … you just don’t know where to look.

“It’s pretty impressive.”

Field surveys complement the app data, measuring slug densities and comparing populations in burned and unburned areas. Surprisingly, slugs in fire-affected zones have rebounded to levels similar to those in untouched regions.

While it’s unclear exactly how the slugs survived the intense heat, scientists believe they sought refuge deep in rock crevices or underground.

The Mount Kaputar slug belongs to the Triboniophorus genus, which also includes Australia’s largest land slug, the red triangle slug. The park is also home to 11 threatened snail species, such as the Kaputar winged snail, the Nandewar pinwheel snail, and the Nandewar carnivorous snail, highlighting the area’s unique biodiversity.