Red swamp crayfish (Procambarus clarkii)

Synonyms: Cambarus clarkii, Astacus clarkii

Common Names: Red swamp crawfish, Louisiana crawfish, Louisiana red crayfish, red crayfish, crawdad

Description:

Red swamp crayfish (Procambarus clarkii) is a small, lobster-like freshwater crayfish native to the south-central United States and northern Mexico [1]. It is sold for food, aquariums, classrooms, and fishing bait, and has spread far beyond its home range ? it is often called the most invasive crayfish in the world [1]. MISIN tracks it because it burrows into and erodes banks and dams, eats native plants and animals, outcompetes native crayfish, and can carry a disease that is deadly to them [1][2].

Identification:

Red swamp crayfish looks like a small lobster, usually dark red, and grows up to about 5 inches long including its claws [1][2]. Its claws are long and narrow and are covered in bright red, raised bumps, and there is a black, wedge-shaped stripe on the underside of its tail [2]. Younger animals can look darker or grayish [1]. The crayfish digs chimney-like mud burrows along the edges of ponds, ditches, and streams ? holes about 2 inches across with a little "chimney" of mud around the opening ? and digs deeper burrows in dry or cold weather [2].

It is most active and easiest to find from spring through fall, but its burrows show up year-round, and females carrying eggs or young can be seen in any season [1]. The chimney burrows along a shoreline are often the first sign that it is present [2].

At-a-glance cues:

1. Small lobster-like crayfish, dark red, up to about 5 inches long with the claws [1][2]
2. Long claws covered in bright red, raised bumps [1][2]
3. A black, wedge-shaped stripe on the underside of the tail [2]
4. Chimney-like mud burrows along pond, ditch, and stream banks [2]

Habitat:

Red swamp crayfish lives in many kinds of fresh water ? ponds, lakes, marshes, ditches, canals, slow streams, swamps, and even seasonal wetlands [1]. It is very hardy, surviving poor water quality, low oxygen, and dry spells by digging into the bank and waiting out the drought in its burrow [1].

The crayfish is native to the Gulf coastal plain, from the Florida panhandle to Mexico, and the southern Mississippi River drainage [1]. It has been introduced across the United States and around the world [1]. It is an omnivore ? its "menu" includes water plants, snails, insects and other small animals, fish, and the eggs and young of amphibians [1][2].

Reproduction:

Red swamp crayfish spreads mostly through people. It is sold live for crawfish boils, sold as a "freshwater lobster" for aquariums, used as fishing bait, and kept in classrooms ? and it escapes or is dumped into the wild from all of these [1]. It can also crawl overland for short distances between nearby waters [1]. So it can show up in a pond as a released pet, a dumped bait bucket, or a leftover from a crawfish boil.

It breeds remarkably fast. It can reach breeding age in as little as two months, a single female can carry up to about 500 eggs under her tail, and females with eggs or young are found year-round [1]. Because of this, just a few released animals can build a large population in a short time [1]. The keys to stopping it are never releasing it and catching new populations early [1].

Impact and Damage:

For property owners, the burrowing is the headline problem. Red swamp crayfish digs extensive burrows along banks that collapse and erode, and it damages levees, dams, ditches, ponds, and water-control structures [1]. It is not dangerous to people ? it is the same kind of crawfish people eat ? though it can pinch if handled.

For natural areas, it does broad ecological damage. It eats large amounts of aquatic plants and preys on native invertebrates (such as dragonfly nymphs), amphibian egg masses and young, and small fish, and it outcompetes and drives out native crayfish through aggression and fast breeding [1]. It also carries diseases and parasites ? including a fungus, often called "crayfish plague," that is deadly to native crayfish ? which it can spread even where it does not directly compete [1][2]. Together these effects can reshape the food web of a pond or wetland [1].

Similar species:

White River crayfish (Procambarus acutus) is the closest look-alike ? it is also dark red with a black wedge on the tail and bumpy claws, so the two are easily mixed up. The clearest difference is the claw bumps: white on the White River crayfish versus bright red on the red swamp crayfish, and small bumps also cover its shell [1].

Rusty crayfish (Faxonius rusticus) is another invasive crayfish, but it has a pair of dark rusty patches on the sides of its shell and dark bands at the claw tips, not the all-over red bumpy claws and black tail stripe [1]. Virile (northern) crayfish (Faxonius virilis) is a common native that is greenish-brown with bluish claws tipped in orange, lacking the bright red bumpy claws [1]. Marbled crayfish (Procambarus virginalis) is an invasive with a mottled, marbled olive-brown pattern rather than red claws [1].

Monitoring and rapid response:

Signs to watch for:

1. A small, lobster-like, dark red crayfish with bright red bumpy claws and a black tail stripe [1][2]
2. Chimney-like mud burrows along the banks of ponds, ditches, and streams [2]
3. Crayfish found in a pond, water garden, or classroom tank, or caught while fishing [1]

What you can do:

1. Never buy, keep, release, stock, or use red swamp crayfish as bait, and never dump them from aquariums, classrooms, or crawfish boils into the wild [1].
2. If you find or catch one, do not put it back ? keep it, freeze it to kill it humanely, take clear photos, note the exact location, and report it right away (below) [2].
3. Don't move water, mud, plants, or bait between waters, and clean, drain, and dry boots, nets, and gear [1].
4. In a backyard pond, you can set crayfish or minnow traps to catch and remove them and dispose of them on land ? but report the find first so your agency can respond [1].
5. Natural area crews and agencies handle new populations with rapid response ? trapping, draining, barriers, burrow blockers, and monitoring [1].

When to call a professional:

1. Any confirmed population, or burrows damaging banks, dams, or ponds ? removal is a job for your fisheries or natural resources agency.
2. Any water where this crayfish keeps turning up, which may signal an established population. Keeping or moving it is also regulated in many places, so check with your state wildlife agency first.
3. For chemical control options, contact a licensed applicator or your local cooperative extension office.

Report sightings to MISIN. Help track this species' spread by submitting observations through the MISIN web site or the MISIN mobile app (Android, iOS, Windows, and macOS). Photos at multiple angles paired with a precise GPS location are the most valuable data for confirming new occurrences and triggering rapid-response review.

Credits:

1. U.S. Geological Survey, Nonindigenous Aquatic Species Database. Procambarus clarkii (Red Swamp Crayfish) ? Species Profile. nas.er.usgs.gov
2. Minnesota Department of Natural Resources. Red Swamp Crayfish (Procambarus clarkii). dnr.state.mn.us
3. U.S. Fish & Wildlife Service. Red Swamp Crayfish (Procambarus clarkii) Ecological Risk Screening Summary. fws.gov

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