Before about 25 years ago, the species simply did not exist. A single drastic mutation in a single crayfish produced the marbled crayfish in an instant.

The mutation made it possible for the creature to clone itself, and now it has spread across much of Europe and gained a toehold on other continents. In Madagascar, where it arrived about 2007, it now numbers in the millions and threatens native crayfish.

“We may never have caught the genome of a species so soon after it became a species,” said Zen Faulkes, a biologist at the University of Texas Rio Grande Valley, who was not involved in the new study.