This is what they are and the threat they pose

There are eight crustaceans on Michigan’s list of invasive species you need to know about.

One of them is particularly interesting because it wasn’t banned in Michigan until 2020. Marbled crayfish have yet to be detected in Michigan, but they originated in the pet trade industry. They are not native to anywhere and can reproduce by cloning themselves.

Below are the details of eight invasive crustaceans that are either already established in Michigan or the state just wants people to be on the lookout due to the threats they pose.


  • If you think you’ve found one of these invasive crustaceans, you can report it through the Midwest Invasive Species Information Network. Single Click here and look for the insect.

chinese crab

chinese crab (Dave Kelch, Ohio Sea Grant, Bugwood.org)

The Chinese mitten crab has not been detected in Michigan.

This crab is born in a marine environment, migrates to fresh water to live, and migrates back to a marine system to reproduce. In fresh water, they can be found in rivers, streams, estuaries, or bays that are abundant in aquatic vegetation.

They consume detritus, aquatic plants, algae, benthic invertebrates, and salmon, trout, and sturgeon eggs. They are native to the Pacific coast of China and Korea.

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Michigan officials are concerned about this species because their appetite can completely disrupt a food web and may allow them to outcompete native crabs, crayfish and mussels for resources. They also dig burrows, which decreases the stability of stream banks and increases erosion.

They can consume fishing bait, damage or consume catches, damage fishing nets, and clog pumps, grates, and water intake structures. They are also an intermediate host for the eastern lung fluke, which has not been found in any mitten crab collected in the United States.

Tips to identify the Chinese Mitten Crab:

  • Orange brown to greenish brown

  • The claws are covered with hair.

  • The convex and uneven shell reaches the size of an adult palm.

  • Notch between eyes, 4 spines on each side of carapace

Here is where they have been found in the United States: Chinese crabs have been reported from the Chesapeake Bay, San Francisco Bay, Delaware Bay, Hudson River, Columbia River, and Mississippi River, but the only established population is currently in San Francisco Bay, California. .

They could enter Michigan through ballast water or an intentional release.

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water flea hook

water flea hook (Igor Grigorovich, University of Windsor)

The Fishhook water flea has been detected in Michigan.

Tips for Identifying the Fishhook Water Flea:

  • Translucent body with black eyes.

  • Body length: 1-3mm; 6-13 mm including the tail.

  • The tail contains 3 pairs of spikes and an S-shaped hook near the end.

  • Generally in groups of at least 10 individuals.

  • Bunches appear as wet cotton on items such as cables, ropes, and fishing lines.

Hook water fleas eat other species of zooplankton. They live in fresh and brackish water lakes.

They have been reported from Lakes Ontario, Michigan, Erie, Huron, and Superior; Muskegon Lake and Finger Lakes of New York.

They represent a concern locally because their dietary preference puts them in direct competition with native planktivores. Its long tail and spikes make it less attractive to planktivorous fish, so predators are unlikely to control the population. They could have a serious effect on the planktivorous food supply in the Great Lakes region.

killer shrimp

killer shrimp (S. Giesen, NOAA Great Lakes Environmental Research Laboratory)

Killer shrimp have not been detected in Michigan.

Tips for identifying the killer shrimp:

  • Body coloration varies from transparent and striped to a uniform dark color.

  • Body coiled, laterally compressed.

  • Sexual maturity reached at 6 mm in length, males grow larger than females.

  • The first 4 pairs of legs extend downwards and forwards, the next 3 pairs extend downwards and backwards.

  • 2 pairs of antennas.

Killer shrimp live in fresh or brackish water in lakes, rivers, and canals. They can adapt to a wide variety of substrates with a wide range of oxygen levels, temperature and salinity.

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They primarily consume macroinvertebrates, exhibit cannibalistic habits, and occasionally eat young, weak adults of the same species. Interestingly, the killer shrimp has also been known to kill or injure potential prey without consuming it.

They are native to the Ponto-Caspian Basin of Eastern Europe. They have the potential to spread rapidly across the Great Lakes if introduced through ballast water exchange or without ballast on board.

Marbled Norway lobsters

Marbled Norway lobsters (Ranja Adriantsoa (left), Mari-Liis Komets (right))

Marbled crayfish have not been reported in Michigan and are prohibited.

Tips for identifying marbled crabs:

  • A medium-sized crayfish, ranging from 4 to 5 inches in length.

  • A more visible mottled color pattern on its shell or back.

  • Coloration is generally olive to dark brown, but can range from tan to reddish and blue.

  • The claws are thin or narrow.

Marbled Crayfish have been found in streams, rivers, ditches, ponds, wetlands, and retention basins. They can survive in drought conditions by burrowing in the ground. They have been seen migrating over land.

The marbled crayfish originated in the pet trade and nowhere exists as a native wild population. They have become established in the wild in Germany, Austria, Italy, the Netherlands, the United Kingdom, Japan, and Madagascar.

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They are a local concern because they are the only known decapod crustacean to reproduce through self-cloning ability. All individuals are female and have the ability to lay up to 700 unfertilized eggs that develop into genetically identical offspring. They can quickly take over lakes, ponds, and streams.

They feed on algae, plants, snails, and amphibians and can outcompete native species, including fish. Digging can destabilize banks and shorelines.

They are available in the aquarium trade and create a high risk of introduction and spread through the release of unwanted pets. They could be purchased in Michigan before 2020.

red swamp crab

red swamp crab (Saxifrage – Rudmer Zwerver)

The red crayfish has been detected in Michigan.

Tips for identifying the red marsh crab:

  • Dark red with bright red raised spots, they look like small lobsters.

  • Elongated claws and bony exoskeleton.

  • Head elongated with triangular rostrum.

  • 2.2 inches – 4.7 inches long.

These crayfish live in a variety of permanent freshwater habitats. They burrow deep into the substrate and create large mounds of sand and soil called chimneys with a large hole in the center.

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They feed largely on snails, fish, amphibians, and plants. They have established populations in California, Delaware, Illinois, Maryland, Michigan, Ohio, Oregon, South Carolina, Utah, Virginia, Washington, and Wisconsin. Introduced but not established in Alaska, Hawaii, Idaho, Indiana, Nevada, and New York.

They compete with native crayfish species for food and habitat. Their habits reduce the amount of habitat available for amphibians, invertebrates, and juvenile fish. Their excavation can lead to summer blooms of cyanobacteria and eutrophic conditions.

They were potentially introduced through the aquarium trade, classroom release, live bait dumping, or through stocking events.

rusty crayfish

rusty crayfish (Doug Watkinson Fisheries and Oceans Canada (DFO))

The Rusty Crayfish has become established in Michigan waters.

Tips for Identifying Rusty Crayfish:

  • Brown lobster-like body, up to 6 inches with claws.

  • The large claws have an oval opening when closed and black bands at the tips.

  • Mature crayfish have a dark, rusty spot on each side of the shell.

These crayfish live in lakes, streams, and wetlands covered with rocks, logs, or trees. They don’t dig.

They eat two to three times more than native crabs. They eat anything they can find, including plants, snails, clams, insects, other crayfish, fish eggs, and small fish.

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They are native to Ohio, parts of Kentucky, and Indiana. They are found in the Great Lakes states, New England south to North Carolina and Tennessee, western states such as Colorado, Wyoming, and Oregon. Also present in Ontario, Canada.

They are a local concern because they destroy aquatic plant beds. Their diet can affect native populations and ecosystems. They are collected and used as bait and have moved to other bodies of water that way.

spiny water flea

spiny water flea (Bill O’Neill, University of Wisconsin Sea Grant)

The spiny water flea is established in Michigan.

Tips to identify the prickly water flea:

  • Long, straight tail spine twice the length of its body.

  • 1-2 pairs of spikes on tail spine.

  • Overall length: ¼ – ½ inch.

The spiny water flea eats smaller zooplankton, such as small copepods and other rotifers. They can be found among zooplankton in the upper water column of temperate lakes. They can tolerate brackish water and prefer cooler water temperatures.

They are of local concern because they cause major changes in zooplankton community structure, reproduce rapidly, and directly compete with small fish for food. They also foul fishing gear when their tail spines catch on fishing lines.

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Yabby

Yabby (Chameleon)

The yabby has not been detected in Michigan.

Tips for identifying Yabby:

  • Smooth shell.

  • Colors vary from olive green to brown, but are sometimes red, yellow, or black.

  • Crayfish have two enlarged front claws, four pairs of walking legs, followed by four pairs of swimmers (small swimming legs).

The yabby prefers muddy or settled substrates in water with moderate levels of turbidity. They dig burrows, some of which can reach depths of up to 2 meters. Their burrows can compromise the integrity of dam walls and cause problems for farmers.

They eat decaying vegetation, but are likely to eat anything they find, including other barking crayfish from time to time.

They are native to Australia. They are a local concern due to their rapid growth rate, high spawning frequency, long breeding period, and the speed with which they reach maturity.

They could be introduced to Michigan through aquaculture and the aquarium trade.


Do you want to know more about these invasive crustaceans? Click here.


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