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).

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). It is also popular among anglers as bait for largemouth bass (WDFW 2003). 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).

The Sandusky Bay, OH populations likely stem from an attempted introduction to see if they could get a harvestable population established for human consumption (R. Thoma, Midwest Biodiversity Institute, pers. comm.). This species is commercially cultured in the southern U.S., particularly in Louisiana, where industry profits exceed $150 million annually and the fishery is an integral part of the state’s culture and economy (McAlain and Romaire 2011). Alternately, there is a remote chance these red swamp crayfish were introduced from infested Ohio State Fish Hatcheries during a fish stocking event (R. Thoma, Midwest Biodiversity Institute, pers. comm.).

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

Environmental	Socioeconomic

Potential:
Procambarus clarkii has the potential for a wide array of environmental impacts, including food web alteration, bioaccumulation of toxic substances, community dominance, competition with native species for food or space, modification of physical-chemical habitat properties, consumption of native plants and algae, and predation on native species (Savini et al. 2010). Red swamp crayfish has the potential to successfully colonize northern and colder habitats since it has shown to have biological plasticity in its ability to adapt to atypical thermal habitats. This species can and grow and reproduce at temperatures (mean 13°C) once thought to inhibit completion of P. clarkii's life cycle (Peruzza et al. 2015).

The red swamp crayfish has been responsible for dramatic habitat changes (e.g., through burrowing activity) and changes to ecosystem functioning in invaded systems around the world (Gherardi 2007). Procambarus clarkii is a strong competitor with native crayfish species, including the white river crayfish (P. acutus) or the signal crayfish (Pacifastacus leniusculus), and may exclude these species from shelters (Arrignon et al. 1999, Gherardi and Daniels 2004, Mueller 2007). Aggression exhibited by the red swamp crayfish has also been attributed to reduced breeding success among adult California newts and may extend to other amphibians (Gamradt et al. 1997).

Acting as both a shredder and a predator, P. clarkii has the potential to act as a keystone species and dominate energy flow (Pérez-Bote 2004). Red swamp crayfish juveniles can significantly reduce local macroinvertebrate diversity through predation (Correia and Anastácio 2008). Predation on snails and other grazers may lead to increased periphyton biomass relative to macrophytes. In contrast, prey preference for predatory insects promotes grazer populations and instead decreases periphyton density (Alcorlo et al. 2004). The disappearance of newts in California has also been attributed to predation by P. clarkii, particularly on eggs and larvae (Diamond 1996, Gamradt and Kats 1996). Consumption of detritus by P. clarkii can further restructure energy flow (e.g., shortened pathways to top predators, simplified food web structure) through traditional trophic levels in an invaded system (Geiger et al. 2005).

Capable of removing macrophytes from large areas with its cutting feeding behavior (Feminella and Resh 1989, Smart et al. 2002), P. clarkii causes major shifts in habitat heterogeneity and reduces habitat availability for many invertebrates, amphibians, and juvenile fishes (summarized in Alcorlo et al. 2004, Nyström 1999). Herbivory in red swamp crayfish has also been found to have a significant impact on aquatic macrophytes and periphyton (Elser et al. 1994, Lodge 1991, Matthews et al. 1993, Weber and Lodge 1990) and to change the relationships of benthic insects with plants (Hanson et al. 1990, Lodge et al. 1994). Extensive removal of macrophytes is proposed to have led to local extinction of two snails (Lymnaea peregra, L. stagnalis) and three plants (Myriophyllum alterniflorum, Utricularia australis, Ceratophyllym demersum) in Spain (Montes et al. 1993), but direct predation on the snails may have contributed to the snails’ disappearance (Alcorlo et al. 2004). Herbivorous bird populations (e.g., ducks) have also been severely impacted by the Spanish introduction of P. clarkii (Rodríguez et al. 2005). In Kenya, it has been suggested that populations of the water lily Nymphaea nouchalii var. caerulea declined in Lake Naivasha as the result of P. clarkii herbivory (Hofkin et al. 1991, Lowery and Mendes 1977).

The red swamp crayfish builds its burrows at the water’s edge, and collapse is common on soft sediment banks when burrows are abandoned (Barbaresi et al. 2004). Burrowing activity can impact the nesting ground of demersal fish (Lowery and Mendes 1977). Foraging and burrowing behavior in P. clarkii can also lead to changes in water quality and increased nutrient release from sediment, which in turn may induce localized summer cyanobacteria blooms and eutrophic conditions (Angeler et al. 2001, Duarte et al. 1990, Geiger et al. 2005, Nyström et al. 1996, Yamamoto 2010). Alternately, burrowing activity can suspend sediments and increase water turbidity, reducing light penetration and leading to diminished primary production (Anastácio and Marques 1997, Angeler et al. 2001, Rodríguez et al. 2005).

Many crayfish, including P. clarkii, transmit heavy metals among different trophic levels of the food web. Enriched levels of heavy metals or pesticides in crayfish organs or tissues are transferred to consumers (Otero et al. 2003). The red swamp crayfish has also been characterized within its invaded range as a host to high impact parasites (Mastitsky et al. 2010). It harbors numerous flatworm parasites that may be passed on to vertebrates and can carry the crayfish plague fungus (Aphanomyces astaci) as a chronic or latent infection (Huner and Barr 1991, Longshaw 2011). Procambarus clarkii has been implicated in the spread of this fungus to native crayfish in Europe following initial introduction by the signal crayfish (Barbaresi and Gherardi 2000, Mastitsky et al. 2010). North American crayfish species, however, appear to be resistant to the crayfish plague (Huner and Barr 1991). The white spot syndrome virus, which has caused mass mortalities among shrimp in Europe, can also be carried by P. clarkii (Longshaw 2011).

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

Potential:
The red swamp crayfish is classified as a pest in many countries (Hobbs et al. 1989). Procambarus clarkii has had devastating effects on international rice production, preferentially consuming seedlings following rice field flooding and planting, as well as causing water loss and bank collapse due to its burrowing activity (Anastácio et al. 2000, 2005; Correia and Ferreira 1995). In areas prone to water level fluctuation—such as around dams, levees , or irrigation systems—complex, deep burrows or numerous simple burrows are especially likely to damage these structures through bank destabilization. Where water levels are more constant (e.g., reservoirs, marshes), burrows tend to be shallow and simple (Correia and Ferreira 1995). Foraging and burrowing behavior in P. clarkii can also lead to changes in water quality and increased nutrient release from sediment, which may induce localized summer cyanobacteria blooms and eutrophic conditions (Angeler et al. 2001, Duarte et al. 1990, Geiger et al. 2005, Nyström et al. 1996, Yamamoto 2010).

Predation on fish eggs (e.g., lake trout, Mueller et al. 2006), food competition with commercial fish species, and destruction of fishery nesting and nursing grounds can negatively affect the fishing industry (summarized in Geiger et al. 2005). In Kenya, the red swamp crayfish has been implicated in the destruction of fishing nets and significant reduction in yield due to damaged fish (Lowery and Mendes 1977).

Through accumulation of heavy metals and cyanobacteria toxins (e.g., microcystin), the red swamp crayfish facilitates biomagnification of these harmful materials and their trophic transfer to humans (Gherardi and Panov 2006). In parts of the world, undercooked P. clarkii may transmit parasites to humans, including lung fluke (Paragonimus westermani) and rat lungworm (Angiostrongylus cantonensis) (Matthews 2004). Domestically, Louisiana populations of the red swamp crayfish have been found to harbor another lung fluke, P. kellicoti (Huner and Barr 1991).

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

Potential:
While a major commercial fishery exists both domestically (native populations) and abroad (introduced populations; e.g., Ackefors 1999, Barbaresi and Gherardi 2000), a red swamp crayfish fishery has not been established in the Great Lakes. However, the red swamp crayfish is popular in the live trade market. This species’ striking red color has lead to commercial advertisement as freshwater “lobster” for aquariums (Simon et al. 2005). It is also popular among anglers as bait for largemouth bass (WDFW 2003) and is readily available though the biological supply trade (Larson and Olden 2008).

Procambarus clarkii has the potential to serve as a new food source in invaded ecosystems (Savini et al. 2010). In Europe, it has been suggested that high densities of the red swamp crayfish may lead to greater numbers of herons, egrets, and cormorants (Barbaresi and Gherardi 2000, Rodríguez et al. 2005).

The red swamp crayfish has been proposed for use as a bioindicator of heavy metals (As, Cd, Cr, Pb, Hg, Ni) and organic compounds (as found in fertilizers and pesticides, for example) due to its propensity to accumulate these environmental contaminants (Kouba et al. 2010, Richert and Sneddon 2007). Furthermore, this species may be used in biological control activities. It actively predates chironomid larvae, a rice pest (Correia and Anastácio 2008). In Kenya, P. clarkii consumes and competes with the snail vector of schistosomiasis and has thus been used there as a biological control agent (Lodge et al. 2005).

Among the Great Lakes states and provinces, Minnesota requires a permit for import of live crayfish  and prohibits the transport of crayfish between water bodies and the sale of live crayfish as bait or for use in aquaria (MNDNR 2014). Wisconsin prohibits the release of live crayfish into and waters of the states as well as the possession or use of live crayfish as bait on inland waters other than on the Mississippi River (WIDNR 2015). In Ontario, live crayfish may only be used as bait in the waters from which they were caught; they may not be transported overland, including imported for use as bait (OMNR 2012).  Procambarus clarkii is prohibited in Ontario (regulatory amendments to Ontario Regulation 354/16 under the Invasive Species Act, 2015).  

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).

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

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). 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). It is unlikely, however, to extirpate populations.

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).