Six babies born to a 11-year-old reticulated python at the Louisville Zoo have only one parent—they are the result of a virgin birth. The python, 200-pound, 20-foot-long Thelma, had never been near a male snake during her four-year tenure at the zoo.

When Thelma laid 61 eggs, puzzled zookeepers assumed she had stored sperm from a pre-zoo encounter. But a study published this year reveals that the six offspring that survived carry only mother’s genes. They are the product of a quirk of biology that allows fatherless reproduction, a process called parthenogenesis.

Instead of a sperm and egg fusing to create an embryo, these baby snakes came from the fusion of an egg and a polar body— a cell produced as a byproduct of egg development. Normally these polar bodies die.

Thelma’s keepers suspect that the huge snake’s egg-laying was inspired by the excellent living conditions. "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," zoo curator Bill McMahan told National Geographic.

Thelma’s path, while rare, has been trod (and swum and slithered) by other species before. DNA tests have confirmed parthenogenesis in Flora, the Komodo dragon, a Nebraska zoo-dwelling hammerhead shark and other sharks, fish and reptiles. Birds do it and so do bees — domesticated turkeys and Cape bees, specifically. But while human parthenogenesis is theoretically possible, it is very unlikely.

Not all cases of parthenogenisis are a surprise: Certain lizards rely on parthenogenesis to reproduce. Thelma, however, is a first for her species as far as we know.