Self-Cloning Crayfish Have Taken Over a Cemetery in Belgium

The marbled crayfish are all female, reproduce asexually, are all genetically identical, and are a terror to biodiversity.
Self-Cloning Crayfish Have Taken Over a Cemetery in Belgium
A marbled crayfish in an aquarium. Image: Pro2sound via Getty Images

The marbled crayfish is an organism straight from the pages of sci-fi. Now found across the globe, these crustaceans are all female in sex, identical in genetic make-up (making them all clones), and a terror to biodiversity. 

Schoonselhof cemetery in Antwerp, Belgium is the organism’s latest conquest. Hundreds of the creatures can be found in streams and ponds within the grounds and surrounding areas, The Brussels Times reported. Munching and crunching on everything from rotten leaves to snails, the marbled crayfish is stripping away the ecosystem bit-by-bit. 


“Someone apparently had the animal in their aquarium, and then set it free in a canal,” said Kevin Scheers, researcher at the Flemish Research Institute for Nature and Woodland Research (INBO), in an interview with The Brussels Times. “It’s impossible to round up all of them. It’s like trying to empty the ocean with a thimble.”

But this is likely only the start for the cemetery-turned-nativity, as one marbled crayfish can lay more than 700 eggs. 

The species' resilience lies in its reproduction. Marbled crayfish are parthenogenetic (or asexually self-cloning), meaning a female’s eggs require no fertilization. This results in identical genetic material—a marbled crayfish in Belgium is genetically identical to one in Michigan—and a lot of babies. Marbled crayfish also have three sets of chromosomes instead of two. They're thought to have been created in 1995 when two Floridian crayfish, imported to Germany for the aquarium trade, mated. 

These factors allow the species to grow exponentially in the absence of environmental disturbances, and has even made them of interest to cancer researchers seeking to understand the mechanisms behind cell self-cloning.

“In theory, yes, a cloned population would lack the genetic diversity needed to adapt to any future disturbance such as a novel disease or changing environmental conditions which would make them more susceptible to extirpation,” said Dr. Nathan Lucas of the Michigan Department of Natural Resources (DNR), in an email. “In the absence of those disturbances, however, the lack of diversity may not necessarily act as a barrier to establishment or persistence. Some of those effects may only come into play over larger times scales (many many generations) over which adaptation occurs.”


This crayfish is a bite-size powerhouse. The aggressive, rowdy aquatic species can burrow over three feet into the mud which destabilizes shorelines, Dr. Karen Alofs, assistant professor at the University of Michigan, told Motherboard in an email. They also wreak havoc on aquatic vegetation. Both add to a cascading degradation of an ecosystem, which requires swift action. 

“One of the most effective ways for controlling local invasions of crayfish seems to be trapping and manual removal. But these efforts are labor intensive and removals usually need to be maintained over long periods,” said Alofs. “As you can imagine, in the case of marbled crayfish, one remaining individual can rapidly re-establish a population.”

After being discovered in a German pond in 1995, the crayfish even reached Madagascar in 2007. Their population on the island is now in the millions. Some countries like Spain have tried poisoning areas where the species is found. In Belgium this practice is illegal.

In Michigan, it’s a felony offense to possess a marbled crayfish. The species is popular with some aquarium enthusiasts, so the state is taking preemptive measures to avoid instances like those that occured in Belgium. 

“People will have these crayfish in an aquarium and can’t deal with them, and we’re afraid someone is going to dump them out,” said Joanne Foreman, invasive species communication coordinator at the Michigan DNR. “Next thing you know we’ll have just sheer numbers changing water quality with a population explosion.”


Experts universally agree the best way to stop this invasive species is to avoid any introduction in the first place. Michigan has imposed a statewide ban on the species along with multiple other states in the U.S. and the entire European Union. All cite freshwater habitat preservation as the ban’s motivation. 

“Freshwater species are particularly vulnerable to species invasions because they are also threatened by a number of additional stressors simultaneously including pollution, climate change and habitat fragmentation by dams and road crossings,” said Alofs. 

It's not clear yet how officials plan on removing the crayfish, if they're even able. 

Spokespeople for the INBO did not respond to a request for comment.