It all began with one female.

A slough crayfish was fished from the Everglades in the U.S. and taken to an insect fair in 1995 where a hobbyist bought it. Then, for reasons unknown, that slough crayfish became a new species called a marbled crayfish (Procambarus virginalis) after it began reproducing asexually, essentially cloning itself.

Unable to care for the rapidly increasing offspring, the original owner took them to pet shops where other hobby aquarium keepers bought them. Since then, the world has been invaded by that one crayfish's daughters. "That one animal founded the whole species, and now we have billions worldwide," says Wolfgang Stein, a neuroscientist at Illinois State University. He and a team of researchers recently sequenced the genome