Red swamp crayfish/crawfish, Louisiana crayfish/crawfish, Cambarus clarkii Girard, 1852

In reproductively mature males, hooks are present on the third segment (from the base; the ischia) of the third and fourth pairs of walking legs, and the first swimmeret (pleopod) of ends in four projections (terminal elements), with the most anterior terminal end (cephalic process) of this sperm transfer structure rounded with a sharp angle on the outer (caudodistal) margin, which lacks “hairs” (setae) below its tip. Setae on the anterior surface of the pleopod, closest to the terminal elements, have strong angular shoulders. The right pleopod is wrapped around the side, such that it appears reduced or absent, and possesses a spur on the inner margin on its fifth joint (carpopodite) (WDFW 2003). Strong spines project from the inner face of the sixth joint (propodite); “knots” are present on the dorsal face or this joint (Boets et al. 2009).

Juveniles are not red and are difficult to distinguish from other Procambarus species (Boets et al. 2009).

The red swamp crayfish is a physical ecosystem engineer, primarily constructing simple, two-crayfish burrows consisting of a single opening, which may be covered with a mud plug or chimney to reduce evaporative loss further from the water’s edge, and a tunnel widening to an enlarged terminal chamber (Correia and Ferreira 1995, Huner and Barr 1991, Jaspers and Avault 1969). In periods of drought or elevated temperatures, these burrows can extend 40-90 cm down to water table (Ingle 1997). Burrow density is typically greatest in areas with fine sediments and lowest in areas of sand, gravel, or cobble (Barbaresi et al. 2004). Where present, Myriophyllum sp., fallen logs, and other vegetation may encourage greater burrow density (Correia and Ferreira 1995). Water hyacinth (Eichhornia crassipes) has also provided habitat for this crayfish in other introduced populations (Smart et al. 2002).

Like most crayfish, the red swamp crayfish is an opportunistic omnivore, consuming plant material, animals, detritus, and sediment (Alcorlo et al. 2004; Anastácio et al. 2005; Correia 2003; Gherardi and Barbaresi 2007, 2008; Gutiérrez-Yurrita et al. 1998; Hobbs 1993; Ilheu and Bernardo 1993; Pérez-Bote 2004; Smart et al. 2002). In terms of feeding preference, a few trends have emerged from studies of native and introduced populations. Plants and/or detritus tend to be consumed in greatest frequency and volume, with plant consumption highest in summer and detritus feeding intense year round (Correia 2003, Gherardi and Barbaresi 2008). It appears that crayfish may exhibit selectivity for particular plants but not among animal prey (Gherardi and Barbaresi 2007). The animal constituents of the red swamp crayfish diet tend to be dominated by insects (particularly chironomids), other crayfish, mollusks (snails), and fish (Ilheu and Bernardo 1993, Pérez-Bote 2004). Juveniles consume more animals than adults, which exhibit an ontogenic shift in diet to plants and detritus, but cannibalism is most apparent in adults and preadults (Correia 2003, Pérez-Bote 2004). Fish is also an important staple of the adult winter diet, and males may eat fish in a higher proportion than do females. This may be attributed to large claw size in some males and potentially also due to higher male mobility during the mating season (Ilheu and Bernardo 1993, Pérez-Bote 2004). However, the nutritional benefit of carnivory may be outweighed by the cost of active predation, leading to increased herbivory or detritivory in the field (Ilheu and Bernardo 1993). Overall consumption is highest in the fall and winter (Pérez-Bote 2004).

The life cycle of the red swamp crayfish is relatively short, with an onset of sexual maturity occurring in as few as two months and a total generation time of four and a half months (Huner and Barr 1991). Breeding typically taking place in the fall, though in warmer, wetter regions, there may be a second reproductive period in the spring. This species exhibits high fecundity: a 10 cm female can produce as many as 500 eggs, while a smaller female produces around 100 eggs (GISD 2011, Huner and Barr 1991). Egg production make take as short a period as six weeks, followed by a three-week period of incubation and maternal attachment and an additional eight weeks until egg maturation (GISD 2011). Procambarus clarkii females incubating eggs or carrying young may be found year-round, which contributes greatly to the success and abundance of this species, but optimal temperatures are 21-27°C; growth is inhibited below 12°C (Ackefors 1999, GISD 2011). Recently hatched crayfish remain in the burrow with their mother as long as eight weeks and must molt twice before being self-sufficient (Hunter and Barr 1991). Due to the cannibalistic nature of conspecifics in communal burrows, adult molting often occurs in the open, even in the presence of predatory fish (Hartman and O’Neill 1999). The adult red swamp crayfish exhibits cyclic dimorphism, alternating between sexually active and inactive periods, and in the wild typically does not live longer than two to five years (GISD 2011, Huner and Barr 1991, Smart et al. 2002).

The red swamp crayfish exhibits two types of behaviors—one a wandering phase which involves short peaks of high speed of movement, the other an immobile stage during which it hides in its burrow by day and only comes out at dusk to forage. Breeding male crayfish in the wandering phase may travel as far as 17 km from their site of origin within four days (GISD 2011). Nocturnal activity in the stationary phase does not appear to be driven by predatory avoidance (many of red swamp crayfish predators are also nocturnal) or prey capture (mostly herbivorous; Gherardi et al. 2000).

This species’ striking red color has led to commercial advertisement as freshwater “lobster” for aquariums and may have sped up the species’ advance on the west branch of the Grand Calumet River in Indiana and Illinois (Simon et al. 2005).

Other populations in the Great Lakes region are likely the result of unauthorized intentional or unintentional release.  The red swamp crayfish is readily available though the biological supply trade and may be released following classroom or laboratory use (Larson and Olden 2008; Kilian et al. 2012; Smith et al. 2018). The discovery of Procambarus clarkii carcasses near popular fishing locations in Michigan suggests that it is being used as bait by anglers (Smith et al. 2018).. Intended disposal via the sanitary system (being flushed down toilets) is likely to be ineffective, as many P. clarkii has been seen in urban zones around waste water treatment areas, having apparently survived treatment (Indiana Biological Survey 2008).

Procambarus clarkii can survive exposure to air for long periods of time, Banha and Anastácio (2014) report an LT90 of 17.6 hours for red swamp crayfish. Overland migration is an important behavioral trait to consider in the spread pattern of this species (Thomas et al. 2019).

Summary of species impacts derived from literature review. Click on an icon to find out more...

Environmental	Socioeconomic

Procambarus clarkii affects ecosystems by altering food webs, accumulating toxins, outcompeting native species, modifying habitats, and preying on native plants and animals. Its burrowing and feeding behaviors can significantly change habitat structures and reduce biodiversity, posing a threat to native crayfish by excluding them from shelters. As both a shredder and predator, P. clarkii can potentially act as a keystone species and dominate energy flow within ecosystems.

Procambarus clarkii has a moderate socio-economic impact in the Great Lakes.

Classified as a pest, Procambarus clarkii burrowing can damage structures like dams and levees by destabilizing banks. It negatively affects the fishing industry by preying on fish eggs, competing for food with commercial fish species, and destroying nesting and nursing grounds. P. clarkii also facilitates the biomagnification of heavy metals and toxins to humans and can transmit parasites, such as lung flukes, when undercooked.

Procambarus clarkii has a moderate beneficial effect in the Great Lakes.

Although not yet established as a fishery in the Great Lakes, Procambarus clarkii is popular in the live trade market and marketed as a freshwater "lobster" for aquariums. It is used by Michigan anglers as bait and is readily available through the biological supply trade. P. clarkii could also serve as a new food source in invaded ecosystems and has been linked to increased populations of certain bird species, such as herons, egrets, and cormorants, in Europe.

• Illinois: This species is not on the Illinois Aquatic Life Approved Species List and if it is not otherwise native to Illinois it is illegal to be imported or possessed alive without a permit (515 ILCS 5/20-90).
• Indiana: This species is listed as a species of concern in Indiana, however, no specific regulations are defined.
• Michigan: It is prohibited in Michigan and is unlawful to possess, introduce, import, sell or offer this species for sale as a live organism, except under certain circumstances (Natural Resources Environmental Protection Act).
• Minnesota: This species is prohibited in Minnesota and it is unlawful (a misdemeanor) to possess, import, purchase, transport, or introduce this species except under a permit for disposal, control, research, or education (Statute 84D.07).
• Ontario: It is prohibited in Ontario, making it illegal to import, possess, deposit, release, transport, breed/grow, buy, sell, lease or trade this species (Invasive Species Act, 2015).
• Pennsylvania: In Pennsylvania, the sale, barter, possession or transportation of all species of crayfish is banned unless they are transported as (1) Bait on, in, or about the water from which taken or (2) For testing and scientific purposes or restaurant consumption, adequate measures have been taken to prevent their escape and they are accompanied by documentation stating the point of origin and the destination to which they are to be delivered (58 Pa. Code § 63.46).
• Wisconsin: All species of the family Cambaridae are prohibited in Wisconsin and one cannot transport, possess, transfer, or introduce it without a permit (Chapter NR 40, Wis. Adm. Code).

Note: Check federal, state, and local regulations for the most up-to-date information.

Control

Physical, chemical, and biological management options have been proposed for the red swamp crayfish (Hyatt 2004).

Physical: While not likely to eradicate a population, unless the population is quite small and has a limited range, physical control methods (e.g., traps, fyke and seine nets, electro-fishing) provide an option for population reduction (GISD 2011). Intensive trapping campaigns have been suggested to be safer and more profitable (for fisherman) than biological or chemical treatments (Barbaresi and Gherardi 2000). However, traps tend to attract larger (often reproductive male) crayfish, while frightening off smaller individuals (Aquiloni and Gherardi 2008). As with other methods of physical control, trapping on its own is unlikely to eradicate a crayfish population and must be maintained for lasting effects for be realized (Barbaresi and Gherardi 2000, Kerby et al. 2005). Short-term trapping efforts may stimulate biological feedback responses, including shorter time to reproductive maturity and higher fecundity (GISD 2011).

Natural and artificial barriers, in combination with high flow velocities and/or steep banks, can reduce the upstream spread of red swamp crayfish (Kerby et al. 2005, Lemmers et al. 2022). Research suggests that electric barriers may prevent upstream movement (Egly et al. 2021)

One population in Wisconsin was successfully eradicated by filling the invaded pond (Bunk and Van Egeren 2016).

Chemical: Possible chemical control mechanisms include biocides, pesticides, general toxins, and pheromones, with only the latter being crayfish-specific (Hyatt 2004).

Carbon dioxide shows promise as a tool to drive crayfish toward traps increasing capture rate (Fredricks et al. 2020) . It is not likely to be 100% effective by itself, but could be a useful component of an integrated management strategy (Abdelrahman et al. 2021); though Smerud et al. (2022) demonstrated that open-water treatments are possible.

Water treatment with derivatives of pyrethrum appears to be more effective than spraying burrows (Gherardi et al. 2011). This insecticide breaks down rapidly in sunlight, is harmless to plants, and has a low toxicity to birds and mammals; however, it is also toxic to fish, insects, and other crustaceans (Peay et al. 2006). Tests of cypermethrin and deltamethrin indicate they are highly toxic to crayfish with only short-term persistent and low bioaccumulation (Lidova et al. 2019). Other insecticides that have been effective in treatment of red swamp crayfish-infested waters include fenthion and methyl parathion (Chang and Lange 1967), but these have led to the simultaneous decline in bird populations (MacKenzie 1986).

Use of pheromone attractants to trap red swamp crayfish is currently inconclusive but may be an effective tool in early detection of new invasions in small, confined water bodies (Gherardi et al. 2011). While molt and reproduction regulating hormones (ecdysteroids) control aggression in P. clarkii¸ they are not species specific or cost-effective when applied to wild populations (Gherardi et al. 2011). Application of non-ionic surfactant is also not effective in the field (Anastácio et al. 2000).

Biological control: Biological control experiments in Italy have found that the European eel (Anguilla anguilla) will prey upon small-sized or soft crayfish, providing a potential complement to trapping in closed systems (Aquiloni et al. 2010). However, eels also prey on fish eggs, fry, amphibians, and reptiles (Geiger et al. 2005). Similarly, smallmouth bass, rock bass, largemouth bass, perch, and pike will prey on smaller crayfish (Geiger et al. 2005). In addition to direct predation, the presence of predatory fish in crayfish habitat acts to limit crayfish feeding activity (Aquiloni et al. 2010).

Integrated management: Release of males partially sterilized with 20 Gy ionizing irradiation, a process which reduces testes size and alters spermatogenesis, may contribute to population reduction, decreasing reproductive success (number of hatchlings) by 43% in a test study (Alquiloni et al. 2009). Best success is achieved using medium and large sized males (Hamasaki et al. 2022). Sterile male programs are unlikely, however, to extirpate populations.

Regulatory control: Smith et al. (2018) found that the number of retail shops selling live P. clarkii actually increased following prohibition, highlighting the importance of industry cooperation.

For more information on management of invasive crayfish in the Great Lakes region, please visit the Invasive Crayfish Collaborative.

A population of crayfish originally identified as Procambarus clarkii from the Seneca system, New York was later verifed as Procambarus acutus (11/28/2017).