What happened to the slough crayfish is every macho man's nightmare. A genetic glitch allowed one female to begin cloning herself, and because these females are larger and more prolific, they started to take over. A new study argues that these clones constitute a new species—one where every individual is genetically identical. The all-female clones were first discovered in 1995 by German pet traders and quickly became a popular addition to home aquariums. Later, they escaped into the wild, where they have become a threat to native crayfish in several places, including Madagascar. Genetically, the clones—known as marbled crayfish because of their appearance (see image above)—are similar to slough crayfish (Procambarus fallax), which are found in Florida and Georgia, except they have three sets of chromosomes instead of the typical two. In the new study, published this month on the bioRxiv preprint server, researchers show that the slough crayfish males can’t fertilize marbled crayfish eggs, a hallmark of a species split, and that the clones contain enough genetic differences to justify designating them a separate species. Generally, new species arise gradually over long periods of time, but the genetic studies indicate that in this case speciation was virtually instantaneous, something that happens in plants but is very rare in animals. And the marbled crayfish is the only one among its 14,000 crustacean relatives able to clone itself. Differences in chemical modifications of the two species' DNA seem to account for the superior size and fecundity, the group reports. The researchers are now analyzing these so-called epigenetic differences in more detail and are proposing this new species be called Procambarus virginalis—the virgin form of the genus Procambarus.