The aphrodisiac that unlocked the secret sex life of snails

Toilet rolls didn’t cut it. Nor did PVC pipes. But sterilised palm fronds turned out to be the perfect aphrodisiac for a rare species of Norfolk Island snail thought to be extinct until five years ago.

Fifteen specimens of Campbell’s keeled glass-snail (Advena campbellii) have multiplied into 800 in four years in a captive breeding program at Taronga Zoo Sydney.

Next week, 600 of the gastropods will be placed in tanks packed into eskies and flown back to Norfolk Island for eventual wild release.

Snails are hermaphrodites, but that doesn’t mean they don’t have sex. Some species are capable of self-fertilisation, but sexual reproduction ensures genetic diversity.

Tarryn Williams Clow, senior keeper at Taronga Zoo, said these snails were “very secretive” about their sex lives.

Parnee Bonson from Taronga Zoo with a species of snail from Norfolk Island that nearly went extinct. Credit: Steven Siewert

“In all the years that we’ve had them here at Taronga Zoo, not once has any keeper really seen them mating,” Williams Clow said. “We think maybe once we got a glimpse, but they’re very private little snails.”

What the keepers have witnessed is the snails giving birth to live young with fully formed shells through a genital pore on their necks.

Dr Isabel Hyman, research scientist at Australian Museum, said similar species of snails have sex.

“Even as hermaphrodites, they would mate and they would exchange sperm, and then both animals would be pregnant at the end of that,” Hyman said.

“In some species, the penises are everted [turned inside out] and entwined together, and they exchange sperm at the tips of the penis. In others, it’s internal.”

Hyman said the project started when she was sent photos of a snail on Norfolk Island and recognised it as a species thought to be extinct.

She and a colleague flew to Norfolk Island to see the creatures, squeaking home the day before Australia went into COVID-19 lockdown.

The breeding program has increased the population in captivity from 15 to 800, and snails will now be released back to the wild on Norfolk Island.Credit: Steven Siewert

In 2021 Hyman returned with funding to collect snails for a breeding program to create an insurance population.

The snails swapped the subtropical rainforest of Norfolk Island for a humidity-controlled room behind the scenes at the zoo.

Williams Clow said it was a steep learning curve to figure out how to care for the snails.

“They were originally feeling quite optimistic when the snails arrived … we had all these babies,” Williams Clow said. “We soon learnt that they were actually premature because they were so stressed.”

The scientists also brought over a second species, Advena suteri, but too many died in captivity.

Illustration by Matt Golding

Once the keepers got the diet right, the Advena campbellii survived to adulthood. Yet, they were still not breeding.

The keepers needed to ensure the snails could rest, including “aestivation”, where they pull fully inside their shells to rest and conserve moisture.

“We tried everything from PVC pipes to toilet rolls,” Williams Clow said.

The key turned out to be palm fronds – collected from the ground around Taronga but sterilised because the snails are in quarantine. In the wild, the adult snails live under palm fronds.

The museum and zoo teams will hand the 600 returnees to Norfolk Island National Park rangers and a PhD candidate from Western Sydney University, another project partner.

The snails will be in quarantine on the island for another five weeks, and slowly weaned to a natural diet, then released to the wild.

Hyman said the scientists have learnt enough to try again with Advena suteri or a third species, Fanulena imitatrix.

She said all the native snails were historically affected by land clearing and the main threats now were introduced rats and feral chickens.

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