No one knows exactly when the clones first appeared, but humans only became aware of them in the early 2000s.
It was a German aquarium owner who first brought it to scientists’ attention. In 1995, he had acquired a bag of “Texas crayfish” from an American pet trader, only to find his tank inexplicably filling up with the creatures. They were all, it turns out, clones. Sometime, somewhere, the biological rule that making baby crayfish required a mama crayfish and papa crayfish was no longer inviolate. The eggs of the hobbyist’s all-female crayfish did not need to be fertilized. They simply grew into copies of their “mother”—in a process known as parthenogenesis.
Crayfish specialists were astonished. No one had seen anything like it. But the proof was before their eyes and in 2003, scientists dubbed the creatures marbled crayfish, or Marmorkreb in German.
Scientists quickly realized the marbled crayfish were not just in German aquariums. The self-replicating creatures were out in the wild, and they were aggressive invaders. “Every single one has the ability to reproduce. Every single one could start a new population,” says Zen Faulkes, a crustacean researcher at the University of Texas at Rio Grande Valley who keeps a map of marbled crayfish invasions. You can easily buy marbled crayfish online (though they are now banned in the European Union and some U.S. states). The species has shown up in the wild in Germany, Italy, Slovakia, Sweden, Japan, and Madagascar. “We’re being invaded by an army of clones,” says Faulkes.