Invasive red swamp crayfish are a serious concern because of their ability to damage earthen structures and the threats they pose to the environment.
They're also known as Louisiana crayfish, but they're not welcome in Michigan.
The state's Department of Natural Resources confirmed this week that live invasive red swamp crayfish has been found in two locations — Sunset Lake near Vicksburg and in a retention pond near Novi.
DNR staff found 111 specimens from the retention pond, and "several crayfish" in the shallows at Sunset Lake, according to a news release.
The DNR is concerned about the discoveries, which are the first in the state since 2015, when several dead crayfish were found in Allegan County (no live specimens were found, however).
Here's a Q&A from the Michigan DNR on why the agency is concerned:
What are red swamp crayfish?
Red swamp crayfish, also known as Louisiana crayfish, are deep red in color with bright red, raised spots covering the body and claws. They have a black, wedge-shaped stripe on the top of the abdomen. Between 2 and 5 inches in length, these crayfish resemble miniature lobsters. They are native to the Mississippi River drainage and the Gulf Coast and are the popular "crawfish" or "crawdads" used in southern cooking.
Why are they a concern?
Red swamp crayfish are a serious concern because of their ability to damage earthen structures and the threats they pose to the environment.
"Eradicating red swamp crayfish is very difficult," said Nick Popoff, aquatic species and regulatory affairs manager for the DNR. "They dig deep burrows near lakes and rivers and can spread quickly over land." Popoff said that such burrows, which can be more than 3 feet deep, can cause damage (through bank destabilization) to infrastructure such as dams, levees, irrigation systems and personal property. In Wisconsin, the only solution for one instance of a red swamp crayfish invasion was an extreme measure to pave over a pond.
Red swamp crayfish are considered invasive in Michigan because they compete aggressively with native crayfish species for food and habitat. They feed on plants, insects, snails, juvenile fish and other crayfish, disrupting the food chain for many aquatic species.
Red swamp crayfish can survive drought conditions and are known to migrate as much as approximately 2 miles over land in search of habitat. They are very fertile, with females laying up to 600 eggs at a time and reproducing up to two times in a year.
How did red swamp crayfish get here?
Sources of the two infestations are not known, but according to Popoff, live crayfish may have been brought from southern states for use as bait or for human consumption. Red swamp crayfish also are sold in some states as personal or classroom aquarium pets, and release of those pets is one way invasive species are spread.
"Red swamp crayfish are a prohibited species in Michigan, which means it is unlawful to possess, introduce, import, sell or offer them for sale as a live organism, except in special circumstances, including providing specimens to the DNR for identification," said Popoff.
What is being done?
Department staff will continue survey and removal efforts on Sunset Lake and its tributaries to determine the size and extent of the infestation. Staff will be out during the daytime and evening hours setting nets and crayfish traps and using electrofishing equipment to capture and remove the crayfish. Connecting water bodies including Austin, Barton and Howard lakes will be surveyed in the coming weeks. Survey and removal efforts are ongoing at the Novi location.
How can people help?
"These two cases show the importance of citizen involvement in the fight against invasive species," said Popoff. "Alert citizens noticed something unusual and reported it to the DNR, allowing us to initiate a quick response to each situation."
Residents and visitors to the Sunset Lake area are asked to try to capture any red swamp crayfish they find and place them in a container in the freezer, then report the location of the find to the DNR at 269-685-6851, ext. 0, or by email to firstname.lastname@example.org.
Sightings of red swamp crayfish in the Novi area or elsewhere in Michigan should be photographed and reported with the date and location of the find to email@example.com.
For more information about red swamp crayfish and other invasive species of concern in Michigan, visit www.michigan.gov/invasivespecies.