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Harmful Impacts
Harmful Impacts
Red swamp crayfish (RSC) and marbled crayfish compete aggressively for food and habitat with native amphibians, invertebrates, and juvenile fish. Burrowing and foraging behavior can also lead to erosion, summer cyanobacteria blooms, and eutrophic conditions.
Both crayfish are on the Michigan invasive species watch list and are prohibited species, which means it is unlawful to possess, introduce, import, sell or offer that species for sale as a live organism.
Local Efforts
Local Efforts
RSC were discovered in Shelby Township in 2019, and Washington township in 2022. In 2024 the CISMA performed landowner outreach, surveys and removal efforts resulting in 659 crayfish being removed from local waterways.
The CISMA will continue early detection and rapid response efforts in 2025. Specific county drains, ponds, and lakes in Shelby and Washington Township will be targeted. Survey and removal efforts can only take place where landowner permission is provided. To provide permission, please email CISMA@macombgov.org.
How You Can Help
How You Can Help
Report observances to the Midwest Invasive Species Information Network (MISIN) or notify your local CISMA.
Reduce Invasive Pet and Plant Escapes (RIPPLE) and never be release pets into wild waterways.
Dispose or trade any unwanted fish or crustaceans.
Although not legal for sale in Michigan, RSC and marbled crayfish can express a variety of colors which make wrongful identification in retailer shops a possibility.
Red swamp crayfish
Red swamp crayfish
Dark red color or olive with bright red raised spots
Closed carapace (two plates on back touch)
Native look-alikes:
Devil crawfish: mostly tan body with red highlights around head, body, and claws
White river crayfish: color may vary from tan to rusty red color, no bright red bumps
Marbled crayfish
Marbled crayfish
Not yet detected in Michigan
Marbled color pattern most visible on its carapace or back
Coloring is generally olive to dark brown but can be tan to reddish to blue
Reproduces through parthenogenesis (i.e., ability to self-clone)
all individuals are female
up to 700 unfertilized eggs that develop into genetically identical offspring
If you see marbled crayfish in the wild, take one or more photos and make note of the location, date and time of the observation, and report to:
Lucas Nathan, DNR Fisheries Division, nathanl@michigan.gov 517-599-9323
Native look-alikes:
Calico crayfish: small (2” to 3.5”) and generally grayish-green in color. Claw tips or pincers are orange, and purple-tinged in adult males.
White river crayfish: have larger, more rounded claws. Both claws and carapace are covered with raised bumps or tubercles.
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