A global invasion is underway. A 10-legged mutant crayfish is on the march throughout the world.

They’re all female. They don’t need males to fertilise their eggs. And they’re proving remarkably resilient and adaptive.

Now they’re threatening the destruction of native freshwater species and the devastation of entire ecosystems.

After 20 years of the crustacean’s blitzkrieg through Europe and Africa, science now knows where the monster came from. An analysis of the mutant’s genome supports fears the marbled crayfish is the result of an unexpected accident in a German aquarium in 1995.

VIRGIN BIRTH

It’s believed a slough crayfish (Procambarus fallax) was imported from Florida as a pet.

According to National Geographic, the new owner added it to an aquarium — but had no idea what was going on under his nose.

The Florida crayfish soon had a surprise for the household — offspring.

He had no idea the clutch was the result of a DNA glitch.

One abnormal egg or sperm must have retained two copies of its chromosomes instead of the usual one. The resultant genetic combination produced a new all-female species capable of asexual reproduction — a phenomenon called parthenogenesis.

And they rapidly began to reproduce.

So fast, in fact, the owner didn’t know what to do with them.

So he took them to local pet shops where other aquarium hobbyists bought them.

Some of these mutant crayfish then somehow managed to escape into the environment.

While not confirmed, this appears to have been the beginning of the march of a new invasive pest.

They’ve marched through Europe and Madagascar, and can be found in Japan.

THE NUMBER OF THE BEAST

The story was revealed after German researchers tracked the genome of a dozen or so marbled crayfish (Procambarus virginalis) back to the original female.

They were surprised to discover the three sets of chromosomes. Most animals receive just one from each parent. The extra set of chromosomes is believed to reduce the chances of genetic mutation, and help the new species adapt to new and challenging environments.

Essentially, the marbled crayfish can pick and choose from its vast genetic library to suit the conditions it finds itself in.

This means they can live in pure or polluted water. They can also eat just about anything — from rotten leaves through to snails, small fish and insects.

Researchers counted 3.5 billion base pairs in the crayfish genome, which makes it about seven per cent larger than the human genome.

“We could detect only a few hundred variants in a genome that is larger than the human genome. That is an incredibly small number,” German Cancer Research Center researcher Frank Lyko says. “If we had more than one animal as a founder, we would have greater genetic differences.”

FRINGE BENEFITS

It is hoped the genetic behaviour of the crustacean will help provide an insight for the behaviour of various cancers. Tumours are able to adapt to their environment, such as developing resistance to drugs, in a similar way the crayfish use their stored DNA to suit the conditions they live in.

“What we see in slow motion with the marbled crayfish evolution is something that happens during the very early stages of tumour formation,” Lyko says.

“In many ways, the invasive expansion of [the marbled crayfish] is analogous to a cancerous lineage spreading asexually at the expense of its host,” Jean-François Flot, an evolutionary genomicist at the Free University of Brussels, told the magazine Science.

But the marbled crayfish’s blitzkrieg continues.

Scientists are keeping track of its advance in the hope some form of counter-strike can be found. Its sale has already been banned in the European Union. Marbled crayfish must not be kept as pets, sold or distributed in any way.