Tracking Michigan crayfish

By Mike Scott

There are several hundred species of crayfish in North America, but one invasive species of crayfish is getting an outsized amount of attention from water biologists and agencies around Michigan and Oakland County. That’s because officials are doing everything possible to prevent the spread of red swamp crayfish, which cause havoc on local ecosystems.

Most other crayfish in Oakland County are native to the region, but invasive species are under constant surveillance by state agencies and researchers.

Crayfish are not technically fish. They are categorized as crustaceans, which makes them more closely related to lobsters, crabs and shrimp. Crayfish do not have a backbone and are invertebrates. They are identifiable by their hard outer shell, also known as an exoskeleton, 10 jointed legs, and two large claws. The most common fish in Michigan, like walleye, trout, perch, and bass, are vertebrates. While crayfish have gills, some species can survive long periods outside of water.

Among the hundreds of crayfish species are relatively consistent features and characteristics. Crayfish generally eat a lot and serve as food for many other aquatic or land species. As one Michigan-based expert put it, crayfish are a “diversity hotspot” with the country’s ecosystems because of the chaos they offer – both good and bad.

“They are an active species,” said Brian Roth, Ph.D., a professor in the Department of Fisheries and Wildlife at Michigan State University. “They eat many things, and many living things eat them. (Native) species are necessary to our water (environments) in Michigan.”

It is generally accepted that there are over 500 crayfish species worldwide, and around 350 to 400 species that live in U.S. That means the U.S. is home to nearly 70 percent of the world’s known crayfish species, representing the highest diversity on the planet for the freshwater crustaceans, according to a 2024 publication released by the Virginia Cooperative Extension, which incorporates fishery and wildlife departments at Virginia State University and Virginia Tech.

Both native and invasive crayfish species are found in lakes and water bodies throughout Michigan and Oakland County. While this region may not have hundreds of crayfish species, it does have more than 50 currently living in Michigan, Roth said. He has been studying crayfish for more than 25 years and is considered one of the state’s foremost experts on the species. Most of those crayfish species are native to the state, but a few are invasive. Invasive species generally find their way to Michigan from other parts of the world with the help of humans who move them to water for one of many reasons.

A crayfish does not have to originate in Michigan to be considered “native.” Roth says “invasive” species are defined as such based on the adverse impact they have on the ecosystem. The majority of crayfish species in Michigan are native. Invasive species are introduced from other areas of the world by humans, with some being more harmful than others.

“(A species) is invasive if they do harm to the ecosystem or the economy of a region,” Roth says. That can include damaging a commercial fishing community, which is possible in Michigan but more common in other parts of the world. “A species can be non-native and not invasive. It mostly depends on their impact.”

The Michigan Department of Natural Resources (DNR) is actively tracking around 10 species of crayfish in Michigan, said Kathleen Quebedeaux, a fisheries biologist with the state agency. Those 10 species include both native and invasive crayfish that are either highly prevalent or of significant concern to an ecosystem’s overall health.

Not all crayfish in Michigan are prevalent in southeastern Michigan, because many inland lakes in the region are shallow compared to lakes in other parts of the state. Many crayfish species can’t thrive in lakes with weedy and sandy water bottoms, but those that burrow into these areas do. They are commonly seen along lake and riverbanks.

“All crayfish are ecosystem engineers,” Roth says, indicating they have an outsized impact on plant and species life around them.

Crayfish are omnivores, which means they eat both plants and animals. Omnivores have flexible diets, allowing them to consume a wide range of food sources. This increases their adaptability, making it easier for crayfish to thrive in new environments. As a result, crayfish generally eat aquatic plants, algae, insects, snails, detritus, which is small decaying organic matter, and dead fish.

“Crayfish can quickly become abundant wherever they show up,” Roth added. Crayfish species native to Michigan and Oakland County are important to the health of freshwater lakes, rivers, streams, and ponds.

The two most relevant invasive crayfish species in the state are red swamp crayfish and rusty crayfish. Like other invasive crayfish species, they can have a broadly adverse impact on aquatic plants and insects.

“They eat everything, and everything eats them,” Quebedeaux said. Snakes, for example, feed on crayfish, while three native burrowing species eat various insects and other small organisms, such as snails, dead fish, and detritus, along with plants and algae — all of which support a healthy ecosystem.

Beyond consuming high volumes of food, invasive crayfish species tend to eat as much protein as possible, Roth added. Fish eggs have high amounts of protein. Since other animals also need protein, crayfish are a desirable meal for not just aquatic-only species, but minks, raccoons, birds, and more, he adds.

The adverse impact on aquatic plants from invasive crayfish is often overlooked, he added. When crayfish eat aquatic plants, species that use such plants as habitat have to find new places to live and breed. That can cause a level of stress that makes it hard for other species to reproduce or even survive. Native aquatic plants can help keep water clear, healthy nutrients in place, and provide important protection for many species – all of which is good for county lakes.

“Aquatic plants are exceptionally important in our ecosystem,” Roth said. “They have very positive effects on everything around us. We don’t want to get rid of them.”

Rusty crayfish are widespread and have been in Michigan for multiple decades, Quebedeaux said. That species is large and often competes with other fish species for food. They can be aggressive toward other species and are generally destructive to their ecosystems, she added. Rusty crayfish arrived in Michigan largely because of their use as bait. Despite being invasive, the state allows residents to transport rusty crayfish because of their high numbers.

“We think it will cause more help than harm to allow (rusty) crayfish to be transported for one reason or another,” Quebedeaux said. “We don’t have a lot of tools to remove them because of how many there are. So, we try to manage their population as best as possible.”

Despite that allowance, rusty crayfish are a regulated species. They appear to have a long history in Michigan, but the population has been rising over the last few decades. Roth says that his department at MSU uncovered data from the 1970s that suggests the population of rusty crayfish has increased exponentially over the last 50 years.

“They have really expanded their range to almost every major river ecosystem in the state,” Roth said. “That was a surprise to us when we dug into the data and really compared the numbers.”

With Roth’s help, MSU conducted a study from 2014-2016 that included more than 90 bodies of water in the state, including lakes, ponds, rivers and streams, which helped to verify the increase in numbers. It lends further proof to the DNR’s decision to manage, rather than eradicate red swamp species. Yet there are other reasons as well. Rusty crayfish stay underwater 100 percent of the time, which makes it more difficult for them to spread to new environments.

They can travel through connected bodies of water but won’t climb out of the water to travel on land. As a result, rusty crayfish don’t commonly spread much from one Michigan lake to another.

The other main invasive species – the aforementioned red swamp crayfish – is a different story. Red swamp crayfish are able to survive outside of water for days, which makes them a popular pet. Their ability to survive outside of water means they can be shipped anywhere in the world. That makes them more apt to spread quickly if not closely monitored.

In fact, red swamp crayfish will move themselves on a local level, especially during damp or humid days. Roth can recall days when he has seen red swamp crayfish get out of a pond on a golf course and walk across a fairway in an attempt to travel to another part of the course, and potentially a different body of water.

“They can walk up to an hour per day, and that’s an issue,” Roth says. “We do not want to have these invasive crayfish moving around on their own. It’s a worry.”

Unlike their rusty crayfish cousins, red swamp crayfish have been prohibited in Michigan since 2014. This means it is illegal for anyone in Michigan to knowingly possess, introduce, import, sell, or offer the species for sale as a live organism, except under certain circumstances.

They first appeared in Michigan in 2017 and are only known to be present in several waterbodies in Oakland County, including ponds and streams. The DNR is actively involved in an eradication campaign against red swamp crayfish, which are native to the southern U.S. and Mexico. These crayfish are often boiled for human consumption and have historically been used as live bait.

Quebedeaux said red swamp crayfish arrived in Michigan for several reasons: interest in their use as live bait, demand in the food trade, and breeding as exotic pets. Some red swamp crayfish display bright colors that appeal to collectors.

They have even been marketed nationally to primary and secondary school teachers as a teaching aid. In that scenario, a teacher may not know how dispose of a red swamp crayfish. Some teachers are not aware that red swamp crayfish are banned in Michigan. Crayfish are considered useful for classrooms because they are durable, observable and instructionally versatile organisms for life-science education.

The North American Association for Environmental Education has identified the use of live crayfish in classrooms as a pathway for the introduction of invasive crayfish into our local waterways. To help address this issue, the association created its Investigating Crayfish and Freshwater Ecosystems curriculum to teach students about Great Lakes ecosystems, the significance of native crayfish, and the ecological threats posed by invasive crayfish.

“The aquarium hobby really likes them because of how colorful they look,” Quebedeaux said.

Unfortunately, many hobbyists soon discover that red swamp crayfish are extremely destructive aquatic pets. “They eat everything in the tank and are very good escape artists,” Quebedeaux said. “Some owners will let them go, and they don’t realize how destructive that can be.”

That is one way invasive species like red swamp crayfish get introduced into a foreign ecosystem and cause havoc. Red swamp crayfish are considered even more aggressive than other crayfish species. They can consume food in a manner and volume that is detrimental to their ecosystem. The DNR website describes red swamp crayfish as having the ability to aggressively out compete native crayfish for food and habitat. The invasive species also have a high reproductive rate and engage in “destructive burrowing along shorelines that can destabilize banks and infrastructure,” the website states.

“They are also destructive to water quality,” Quebedeaux said, adding that their activity can promote harmful algae blooms. “They like to burrow, which can lead to soil erosion. We’re always on alert for new populations of red swamp crayfish.”

Their burrowing may be noticeable to humans because, unlike other types of crayfish, red swamps will build “sloppy” burrows and may not even stay there for more than a day or two. The temporary habitat of a burrowing crayfish is called a “chimney,” and can be recognized by the presence of many silver dollar-sized or larger holes, Roth said. “Sometimes their burrows will look like someone just had an upset stomach,” he added. “It can be obvious.”

“That burrowing can cause a ton of erosion,” Roth said. “It leads to bank slumping and sediment release into the water, which we know is bad for aquatic plants and species. We have a ton of water infrastructure around the state, and burrowing and erosion cause issues with that infrastructure everywhere,” Roth said. This is a “common” problem in places where red swamp crayfish are present.

Michigan DNR is exploring the use of environmental DNA testing to help determine the presence, spread, and source of invasive red swamp crayfish in hatchery ponds and connected waters. While the results of this monitoring are not publicly available, it’s being considered by the DNR as a tool for research and management strategies.

The fact that red swamp crayfish have not spread pervasively beyond manmade ponds and a few other waterbodies is a relief, according to the DNR. While Roth believes the invasive species may exist in more areas of the state than the DNR has confirmed, red swamp crayfish populations are known by the DNR to exist in Kalamazoo, Livingston, Macomb, Oakland, Van Buren, and Wayne counties.

“We want to keep (red swamp crayfish) in these areas,” Quebedeaux said. “We want to educate residents about these harmful species so they can be aware of them as well and the destruction they cause.”

Despite some telltale signs, crayfish are notoriously hard to identify, Roth said. Red swamp crayfish are most often characterized by raised red bumps on their large claws. Humans have to look closely to confirm their identity, because some types of native crayfish have a similar look and can only be identified by their raised black claw bumps. It’s why red swamp crayfish can be mistaken for less harmful, native species.

The Michigan DNR confirmed the presence of invasive red swamp crayfish in a new area last summer - an outdoor muskellunge rearing pond at Wolf Lake State Fish Hatchery in Mattawan, Van Buren County. The agency releases information on red swamp crayfish when needed in an effort to keep residents informed.

Two other crayfish species are prohibited in Michigan, even though the DNR does not believe they currently exist in the state. They include the common yabby, a harmful freshwater crayfish native to Australia, and the marbled crayfish. There have been documented sightings of marbled crayfish in a pond in Ontario, Canada. Because marbled crayfish can reproduce through self-cloning, they are often sought after by fish collectors and hobbyists.

“That’s our number one worry outside of the red swamp crayfish,” Quebedeaux said.

Three of the native species — the Great Plains mud bug, painted hand mud bug, and digger crayfish — are primarily burrowing species. They spend most of their time underground and rarely venture into open water, Quebedeaux said. That is beneficial because their presence helps turn over soil in inland lake environments. These burrowing species can also provide habitat for other important endangered species.

“They all have big claws that allow them to dig and burrow,” Quebedeaux said. “We won’t see them even on warm, rainy days.” In fact, both native and invasive crayfish thrive in streams, rivers, lakes and other wetlands.

Native crayfish species have adapted to the local environment over time and thrive in both slow-moving streams and faster-moving lakes. That makes them difficult to contain, but they don’t cause environmental issues. Both Quebedeaux and Roth described most crayfish species as “escape artists,” portraying them as easily escaping aquariums, natural burrows, and everything in between.

“They are really good at hiding as well,” Roth said.

A main goal for both the DNR and Roth’s team at Michigan State is to eradicate red swamp crayfish, provided there are volume benefits without damaging the environment. “We’ve haven’t eradiacted them fully, but we have gotten close,” Roth says about red swamp crayfish.

To do that, researchers and scientists implement self-sustaining controls in water bodies where the invasive species is present. One of the challenges is that some of these water environments, such as retention ponds and golf course ponds, are not in pristine water condition.

The question that researchers are regularly asking themselves is, “Can we manipulate the system to support native crayfish without doing damage?” Roth says.

Residents can harvest native crayfish with a valid fishing license. They are edible but not commonly consumed in this region. “Even native crayfish are not commonly eaten in this part of the country,” Quebedeaux said.

However, the most common way to make and serve crayfish is by boiling them. Roth spent some time earlier in his career in Louisiana and is familiar with “crawfish boils,” which are popular in parts of the Southeast and the Mississippi River basin. “Crawfish boils are fun, and they taste good,” Roth said. “Eating them is not as integrated into the culture up here, but they are popular may places down south.

One of the most common ways to prepare crayfish for a meal is to boil and prepare them. After up to five minutes of boiling, seafood enthusiasts can twist and peel off their tails, usually dipping them in butter or sauces. Crayfish tails are also served on rice, pasta, and other items, although more prevalent in the South.

“We encourage people to enjoy native species up here, and that includes crayfish,” Roth said. “You just need to (research) how to prepare them.”

Because crayfish native to Michigan are not harmful to the local environment, they may be used as bait according to state law. However, Quebedeaux recommends that if released, any crayfish should be returned to the same body of water where they were caught.

The good news is that crayfish native to Michigan are generally doing well, according to Quebedeaux. They help limit invasive activity and protect important native habitats for other species. Native crayfish thrive along natural shorelines but struggle in waterbodies with concrete or other manmade banks, she added.

“Natural banks are good,” Quebedeaux said. “They help maintain water quality and protect wetlands.”

Roth said that residents should report any activities or instances of potential invasive crayfish to the DNR. Above residents should understand the dangers of introducing invasive crayfish to new environments, especially if acquired at a bait store or aquarium shop. Operators of those businesses should know if a crayfish species they are carrying is native or invasive, but it is up to consumers to help prevent the spread.

“Invasive crayfish should not be introduced into our natural systems, period,” Roth said. One of the ways to humanely euthanize a crayfish that doesn’t belong in this region is to stick it in a Ziploc bag and place it in a freezer for a few hours. That method won’t cause the crayfish pain and doesn’t require a detailed cleanup process.

Maintaining aquatic plants also helps the ecosystem and removing such plants can make it easier for invasive crayfish to thrive. Roth understands that many lakefront property owners would ideally remove some aquatic plants for a better view of the lake from their house, or to provide more room for water skiing and other lake-specific sporting activities. But removing natural barriers can harm the water table, causing further issues for local residents.

“You want to make sure you aren’t removing plants that need to be there,” Roth said. “Too many organisms rely on them, including native crayfish.”

The Michigan DNR publishes the official Michigan Fishing Regulations Guide, which is commonly referred to as the state’s fishing guide. It includes all the rules and legal information you need to fish in Michigan waters. The guide’s regulations section includes rules on using crayfish as bait and harvesting them for personal use. It discusses lawful bait use and restrictions on invasive species. For example, the guide states: “native crayfish may be taken in waters open to fishing and used (with some restrictions), but nonnative invasive species (like red swamp crayfish) are prohibited for bait use.”