Ancient Python Lays Eggs, Apparently Without Male Help

Two of the eggs, which she laid on July 23, are being used for genetic sampling, which will help determine whether the python reproduced sexually or asexually. Snakes are also known to store sperm from an earlier encounter for delayed fertilization, though Mr. Wanner said that was unlikely in this case, as the longest snake sperm storage documented was seven years.

Of the remaining eggs, three are in an incubator at the zoo’s herpetarium, which houses its snakes, lizards, frogs and other amphibians. The two others did not survive.

Dr. Jonathan Lasos, a professor of evolutionary biology at Washington University in St. Louis who specializes in reptiles, said scientists had known for a while that there were some species of snakes and lizards in which no males exist and females reproduce asexually.

“What we didn’t realize until relatively recently is that there are some species who normally are sexual — that is, require a male and a female to reproduce — that can occasionally reproduce without any sperm,” Dr. Lasos said. Kimodo dragons, for instance, have been known to lay eggs asexually, a process called facultative parthenogenesis.

The ball python in St. Louis, which is between four and four and a half feet long and does not have a name, arrived at the zoo in 1961 through a private owner. It was estimated to be about 3 years old at the time. The zoo also has a male ball python that is about 31 years old. They are kept side by side in the zoo’s herpetarium, out of public view, but never come into contact.