Virgin birth has been documented in the world's longest snake for the first time, a recent study says.

An 11-year-old reticulated python named Thelma produced six female offspring in June 2012 at the Louisville Zoo in Kentucky, where she lives with another female python, Louise. No male had ever slithered anywhere near the 200-pound (91-kilogram), 20-foot-long (6 meters) mother snake.

"We didn't know what we were seeing. We had attributed it to stored sperm," he said. "I guess sometimes truth is stranger than fiction."

Virgin births have been observed in other reptiles before, including other pythons and snake species, said James Hanken, a professor of herpetology at Harvard University in Cambridge, Massachusetts.

Fatherless reproduction in animals that normally require two parents is called parthenogenesis.

This phenomenon occurs when polar bodies, or cells produced with an animal's egg that normally die or disappear, behave like sperm and fuse with the egg.

Optimal Conditions

The number of species known to be capable of virgin births—pythons, boas, birds, sharks, and more—has grown significantly in recent years, noted study leader Warren Booth, a biologist at the University of Tulsa in Oklahoma. (See "'Virgin Birth' Record Broken by Hotel Shark.")

For instance, until now, scientists had never witnessed the phenomenon in reticulated pythons.

"Pythons are an old, ancient species. We've seen this in more advanced species like garter snakes," said Booth, adding that the discovery helps scientists learn more about the snakes' evolutionary family tree.

It's still a mystery as to why parthenogenesis happens, though Booth hypothesizes that geographic isolation from males and captivity may have a lot to do with it.

In Thelma's case, her virgin birth may have been triggered by ideal living conditions, zoo curator McMahan speculates. (See "Virgin Birth Expected at Christmas—By Komodo Dragon.")

"It takes a lot out of [pythons] to reproduce, and she had everything she needed. I had fed her a really big meal, 40 pounds [18 kilograms] of chicken. She was living in an exhibit larger than the typical size. There were heat pads. Everything was optimal," he said.

View Images Thelma (above) gave birth in 2012 despite having no contact with a male. Photograph by Kyle Shepherd, Louisville Zoo

No Evolutionary Novelty

Despite having only a mother, Thelma's offspring are all half-clones.

Three of them look like her, retaining her intricate reticulated pattern. The others display a "super tiger" pattern of bright yellow with black stripes.

While the six snakes are all healthy behind glass doors, Booth doubts their ability to survive in the wild as they're "highly inbred and often die early."

Overall, the discovery reveals that there's a lot left to be discovered about parthenogenesis.

"It's something we used to consider an evolutionary novelty," Booth said, "that's much more common than we thought."