top of page

U.S. Teams Gear Up to Stop Tasty Red Invader

Louisiana Red Swamp Crayfish Unwanted in Great Lakes Waters  

Crayfish.  ©giocalde/iStock
Crayfish. ©giocalde/iStock

Not all alien invaders are found in sci-fi books and movies. Some of them, like the red swamp crayfish, are very real and can be very local. 

Nature is filled with ecosystems, many of them delicate, where fauna and wildlife have evolved over time to form a balance. And when something disturbs that balance, the effects can be devastating.  

For instance, when non-native organisms are introduced into an environment, they may cause significant harm to existing wildlife populations, damage infrastructure, and even decimate food chains. Such harmful newly resident organisms are called invasive species.  

All around the world, conservationists, scientists, farmers, and many others are trying to deal with the impact of invasive species, and debate is raging about how best to handle them. Should they be removed or culled? And, if so, how? Or, is it more feasible to adopt a live-and-let-live philosophy and permit the invasives to integrate into the ecosystem as nature finds a way to establish a "new normal" balance within the ecosystem? 

Non-native or Invasive 

Terminology is vital in this debate because not all species introduced into a habitat are invasive. 

The term “non-native species” refers to organisms that are not originally from a particular area but are introduced accidentally or purposely by human activity, or by natural events. 

Many non-native species are harmless or even beneficial to their new home. The humble tomato, for example, is non-native to the United States.

Many non-native species are harmless or even beneficial to their new home. The humble tomato, for example, is non-native to the United States but grows innocuously in many people’s gardens and makes a delicious addition to many dinner plates. 

But other non-native species are, as the US National Parks Service defines them, ones that cause “harm to the environment, economy, or human, animal, or plant health.”  

“Most non-native species are not harmful and may provide economic benefits,” said Joanne Foreman of the Michigan Department of Natural Resources (MI DNR), which is currently engaged in programs to control invasive species.  

“Invasive species cause harm when they out-compete native species by reproducing and spreading rapidly in areas where they have no natural predators and change the balance of the ecosystems we rely on.” 

Dr. Douglas Tallamy.  Courtesy of D. Tallamy/©Rob Cadillo
Dr. Douglas Tallamy. Courtesy of D. Tallamy/©Rob Cadillo

Invasive organisms can also impact the food chain.

Dr. Douglas Tallamy is Professor of Entomology and Wildlife Ecology at the University of Delaware. He says the introduction of certain plants—especially ones that offer little food for insects themselves but crowd out native plants that do—impact native US insect populations to the degree that there are fewer insects and reduced bird populations.

“In North America, 96% of our terrestrial birds rear their young on insects,” Dr. Tallamy told The Earth & I. “This is the problem when you reduce that number of insects. By and large, when you flood the environment with a plant from someplace else, it devastates the food web.”  

A Red Menace

One invasive species that has found increasing fame—or infamy depending on one’s point of view—is the red swamp crayfish.

The Louisiana crayfish ... has established unwanted populations far from home—throughout Europe, Asia, and elsewhere in the US.

Native to the south-central US and northern Mexico, it is known as the Louisiana crayfish. But this edible species has established unwanted populations far from home—throughout Europe, Asia, and elsewhere in the US, including on the southern shores of the Great Lakes in Ohio, Michigan, and Wisconsin. 

Red swamp crayfish are large and aggressive compared with many other crayfish species, and are capable of adapting to a broad range of conditions. One 120 mm (4.7 in) long female can carry over 600 eggs. 

A “crawfish boil.”  ©Lainey Stelly/istock
A “crawfish boil.” ©Lainey Stelly/istock

In the US, one reason they have spread so far is because they are the species most used in the food industry and eaten at crawfish boils. They are also popular as aquarium pets and may be released into waterways by aquarium owners who no longer want them.

But despite the red swamp crayfishes’ harmless appearance, they can have a devastating impact if released into new environments.

According to the Invasive Species Center, the crayfish can cause the accumulation of toxic cyanobacteria by overfeeding on aquatic plants. The cyanobacteria can release toxins and take up more of the water’s oxygen—suffocating other organisms. The crayfish also negatively impact native fish populations by consuming fish eggs, larvae, and aquatic vegetation.

Red swamp crayfish also tend to burrow near the water’s edge, decreasing bank and soil stability, which can lead to increased erosion around water infrastructure, bank slumps, and problems with drainage. This has been observed in Europe and Asia, where there have been cases of catastrophic drainage of wetlands and rice paddies.

‘Bad Things Will Happen’                                                         

The state of Michigan has been trying to control booming populations of invasive red swamp crayfish for six years. In 2017, the species initially found its first Michigan home in a hotel retention pond. The MI DNR spent three years trapping and removing more than 100,000 of them from the pond without ever reaching eradication. But efforts are continuing with new ways being tested in the hopes of making a significant dent in their numbers.

Associate Professor Brian Roth.  ©Courtesy of B. Roth
Associate Professor Brian Roth. ©Courtesy of B. Roth

Dr. Brian Roth is Associate Professor at the Department of Fisheries and Wildlife at Michigan State University. He is working with the MI DNR, US Geological Survey, Cooperative Invasive Species Management Areas, Gun Lake Tribe, and Auburn University to determine the best way of eradicating or controlling the species.

“The Michigan DNR is really keen on maintaining our native ecosystems,” he told The Earth & I

“We really just don’t want to find out what happens if red swamp [crayfish] become widespread and abundant. Almost all signs point to ‘bad things will happen’.”


He said the overall aim of the current strategy was to cull the crayfish and control the populations they cannot eradicate.

“We do not want these crayfish here,” he said. “We value our native animals more than invasive ones.”

His team’s research is looking at novel ways to mitigate or resolve the problem. “We have tried sound to attract crayfish. It works but is too cumbersome and not cost effective. Carbon dioxide didn’t work and was pretty expensive.”

DNR technicians Brennan Wright and Katrina Bauermeister collect crayfish specimens.  ©MI DNR
DNR technicians Brennan Wright and Katrina Bauermeister collect crayfish specimens. ©MI DNR

The team even made traps for juvenile crayfish made from modified shower loofahs, but that too was unsuccessful. He said it was too difficult to implement on a large scale. Currently, biological controls using fish and different types of traps are being explored.

“We always implement these strategies in a scientific framework that helps us to learn what works and what doesn’t, and we always keep in mind that we want a strategy that is easy to implement and not cost-prohibitive,” said Dr. Roth.

The team is currently using a pyrethrin-based chemical that binds quickly to sediment and is non-toxic to mammals and birds but highly toxic to crayfish.


The team is currently using a pyrethrin-based chemical that binds quickly to sediment and is non-toxic to mammals and birds but highly toxic to crayfish. 

“We use this chemical in combination with a bentonite clay product to fill existing crayfish burrows and hopefully trapping crayfish inside. These treatments appear to be the most effective and cost-effective means to reduce crayfish abundances,” he said.

A Different Way of Thinking?

But there are some observers in the invasive crayfish debate who argue that the crayfish should be allowed to co-exist with native species or be dealt with in ways that are less aggressive.

“We need to take a humane, long-term view and learn to co-exist, as some species considered invasive are here to stay,” said Cebuan Bliss, an environmental researcher at Radboud University in the Netherlands.

She is one of the contributors to a report on invasive species published by the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES).

Two coypus.  ©JMrocek/iStock
Two coypus. ©JMrocek/iStock

She pointed to a controversial policy in the Netherlands to use underwater traps to kill animals, like coypu (nutria) and muskrat, that are considered invasive. The traps hold the animal under water until they drown, causing the creature distress and pain. Now, she said, the traps are being phased out in the Netherlands but are still being used in other countries.

Coypu can damage infrastructure. A coypu burrow on bank.  ©Wikimedia
Coypu can damage infrastructure. A coypu burrow on bank. ©Wikimedia

“Slowly but surely, we're seeing more humane methods of managing these species,” she said. “In the United Kingdom, researchers are experimenting with contraception for squirrels. Non-lethal methods of managing invasive animals also include using sound, scent, or physical deterrents.”

While debate is ongoing about the best way to deal with invasive species, there is urgency around the need to get something done. Time will tell if such methods are effective.


*Mark Smith is a journalist and author from the UK. He has written on subjects ranging from business and technology to world affairs, history, and popular culture for the Guardian, BBC, Telegraph, and magazines in the United States, Europe, and Southeast Asia.


Join Our Community

Sign up for our bi-monthly environmental publication and get notified when new issues of The Earth & I  are released!


bottom of page