St. Louis Zoo officials are trying to solve the mystery of how a 62-year-old ball python laid seven eggs without being around a male python for at least two decades.

An expert at the zoo says it’s unusual but not rare for ball pythons to reproduce asexually. Pythons also sometimes store sperm for delayed fertilization.

The zoo says the birth is also unusual because ball pythons stop laying eggs long before they reach their 60s. The python laid the eggs in July.

Three of the eggs remain in an incubator, two were used for genetic sampling and snakes in the other two eggs did not survive,