Once upon a time, the mermaid Ariel dreamed of ditching her fins for feet.

Every day in the real world, twin sisters Abby and Bryn Roberts fulfill the fantasies of people who want to become mermaids.

From a St. Paul studio they work their magic, crafting flesh-like silicone mermaid tails in a rainbow of colors that could fool any beach wanderer or sea-weary sailor.

Forget the sequins-and-spandex you'd see in high school plays. Mermaid wannabes plunk down big money for these lifelike custom fins, which start at $2,500.

Who would pay this much to swim with the fishes?

The "mer"-community worldwide — yes, there is such a thing. They are smitten with the tails designed by this landlocked duo. Adults who perform at Renaissance festivals, aquariums and children's parties are placing orders faster than the sisters' fledgling Finfolk Productions can make them.

"We do look at each other almost every day and say, 'We make mermaid tails for a living,' " Bryn Roberts said.

By sheer accident, the 22-year-old sisters dove into a thriving but hidden mermaid culture, connected by social media and celebrated in pop culture. It's part Disney, part "Splash," part ancient myth — brought to life in shows and conventions around the world with names like MerFest and MerPalooza.

"We've always had this fascination with mermaids," said John Athanson, public relations manager for Weeki Wachee Springs in Florida, a mermaid Mecca of sorts. "There's something just mesmerizing about a pretty girl in a mermaid tail."

But it's not all girls in tails. There are mermen, too.

Bootstrapping mermaids

Becoming a mermaid isn't particularly glamorous.

Donning the second skin calls for awkward wriggling and yanking. Once the tail is on, there are just two ways to move around on land: roll or be carried by a "mertender."

For the sisters, figuring out how to make their first tail took a lot of sweat, molding goop and Google. It's not like there's an instruction manual for this sort of thing.

But when the Minnesota Renaissance Festival put out a call for tails in 2012, the sisters took a stab at it. They drew on their experience as Renaissance Festival performers, channeling their enthusiasm for costuming, theater makeup and prosthetics. Abby admits she dragged the more skeptical Bryn into the project.

"I don't know how we did it," Bryn said.

After seven weeks experimenting in Bryn's garage, they had five lifelike tails.

"They came back with these tails and I was just stunned,"said Carr Hagerman, artistic director at the Minnesota Renaissance Festival.

They've since perfected the process: Each tail is made to measure and takes at least a week to complete. They mold silicon for the body, fins and fluke — the large fin at the end. To make the tails sturdy enough for swimming, they build them around a monofin (a big flipper with foot pockets used by swimmers and scuba divers) that is camouflaged by the fluke. The painting comes last.

Word got out about their tails, mostly through the online forums on MerNetwork.com (of course, mermaids surf the Internet). The sisters set up a Facebook page (now with more than 15,000 followers) and used Kickstarter to pay for additional molds. They traveled to Hawaii to shoot promotional pictures and videos. The next thing the Roberts sisters knew, they were shipping tails overseas — Australia, Singapore, Iceland, France.

"The community is big enough that there is demand, but small enough that word spreads quickly," Bryn said.

By fall 2013, they had both quit school and their other jobs to make mermaid tails full time.

Immersed in 'mer'-culture

This spring, Weeki Wachee called. The kitschy tourist attraction, now a Florida state park that attracts 275,000 people a year, has been home to mermaid shows since 1947. They were wondering: Would Finfolk Productions send some tails for performers to wear in the annual mermaid calendar?

"They have some beautiful, beautiful tails that they lent us," said Athanson. "When these tails came in, you just have to look at them like works of art."

But true appreciation comes from diving in.

"The way you move through the water is so fluid," said Allie Causin of Coon Rapids, who performs as Lyrique the Mermaid wearing a Finfolk Productions tail. She also models tails for the company at mermaid festivals.

Causin is a dancer and fell into "mermaiding" when a friend who performs in Renaissance festivals as a fairy needed some mermaids for a children's book photo shoot.

"That's when we first discovered it was a thing," Causin said.

Mermaid myths have been around for hundreds of years, captured most famously in the fairy tale by Hans Christian Andersen. Athanson, of Weeki Wachee, says he sees interest spike every time a mermaid surfaces in pop culture: Disney's "The Little Mermaid," the 30th anniversary of "Splash," and a 2012 documentary-like science fiction program on the Discovery Channel have all kept mermaids at the surface.

Unusual hobby? Sure. But a few stares or sarcastic comments don't stop Causin from pulling on her tail for a swim at Cedar Lake or a local pool, with or without other mermaids. (In case you were wondering, a group of mermaids is called a "pod.")

"There's just this freedom," she said. "It's very much a way of dancing in the water."

Because the mer-world is fanciful, the Roberts sisters are protective of their clients, especially the mermen.

"People's first reaction is, 'That's different and weird and I don't like it,' " Abby said.

But children don't seem to share those reservations.

When the sisters occasionally don tails, they see it over and over: A girl or boy, usually about 4 years old, hands planted defiantly on hips, turns to a parent and says, "See? I told you mermaids were real."

Katie Humphrey • 612-673-4758