Montana Field Guide

The red swamp crayfish is typically dark red, with elongate claws (chelae) and head, a triangular rostrum tapering anteriorly without a central keel, reduced or absent spines on the side of the shell (carapace) between the head and thorax, and a linear to non-existent dorsal surface between the 2 carapace plates (areola), which converge (Boets et al. 2009, GISD 2018, NatureServe 2018). This species does not resemble any of the native crayfish in the state, and should be easily recognized as an introduced species. These really look like mini lobsters. Montana's native crayfish populations could be seriously impacted by the introduction of a non-native species of crayfish, such as the red swamp crayfish.

The first walking leg (cheliped) bears bright red rows of bumps (tubercles) on its side (mesial) margin and palm (Nagy et al. 2018). 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 (Nagy et al. 2018). Setae on the anterior surface of the pleopod, closest to the terminal elements, have strong angular shoulders (Nagy et al. 2018). The right pleopod is wrapped around the side, such that it appears reduced or absent, and, like all members of the Cambaridae, possesses a spur on the inner margin on its fifth joint (carpopodite). 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 exhibits two types of movements—one is a wandering phase which involves short peaks of long-distance fast movement, the other an immobile stage during which it hides in its burrow by day and only comes out at dusk to forage (Nagy et al 2018). Breeding male crayfish in the wandering phase may travel as far as 17 km from their site of origin within four days (GISD 2018). Nocturnal activity in the stationary phase does not appear to be driven by predatory avoidance or prey capture (mostly herbivorous; Gherardi et al. 2000).

This species lives in a variety of freshwater habitats, including rivers, lakes, ponds, streams, canals, seasonally flooded swamps and marshes, and ditches with mud or sand bottoms and plenty of organic debris (Huner and Barr 1991). Red Swamp Crayfish also frequently colonizes rice fields, irrigation channels, and reservoirs (Correia and Ferreira 1995, Gherardi et al. 1999).

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). The animal portion 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).

This species lives in a variety of freshwater habitats, including rivers, lakes, ponds, streams, canals, seasonally flooded swamps and marshes, and ditches with mud or sand bottoms and plenty of organic debris (Huner and Barr 1991). It exhibits considerable ecological plasticity and is tolerant of a range of salinities up to 35ppt (Bissattini et al. 2015), (2-3 ppt for reproduction), pH (5.8-10), oxygen levels (>3 ppm), temperatures (as long as water in burrows neither freezes nor exceeds 95°C), and pollution levels (Huner and Barr 1991). Although this species is known to have a preference for habitats with water temperature from 21 to 30 °C, (Peruzza et al. 2015) demonstrated that the Red Swamp Crayfish could adapt to atypical thermal habitat, characterized by an annual mean water temperature values of 13 °C. Studies of the red swamp crayfish invasion in Europe suggest that it tends to prefer areas of lower flow velocity and low elevation; in central and southern Europe, it has established in warm, shallow natural and agricultural wetlands while in northern Europe, it can be found in small permanent ponds free of fish predation (Cruz and Rebelo 2007, Henttonen and Huner 1999). 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 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).

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 2018, 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 2018). Red Swamp Crayfish 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 2018). Recently hatched crayfish remain in the burrow with their mother as long as eight weeks and must molt twice before being self-sufficient (Huner and Barr 1991). 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 2018, Huner and Barr 1991, Smart et al. 2002).

The Red Swamp Crayfish exhibits considerable ecological plasticity and is tolerant of a range of salinities up to 35 ppt (Bissattini et al. 2015), (2-3 ppt for reproduction), pH (5.8-10), oxygen levels (down to 3 ppm), temperatures (as long as water in burrows neither freezes nor exceeds 95°C), and pollution levels (Huner and Barr 1991). Although this species is known to have a preference for habitats with water temperature from 21 to 30 °C, it has been shown that the Red Swamp Crayfish could adapt to atypical thermal habitat with annual mean water temperature values of 13 °C. Whether this means that this species could survive a Montana winter is not clear, but with increasingly warmer winter temperatures, the SE corner of the state may be an area suitable for invasion, if released.

Threats to Montana's native crayfish populations could be seriously impacted by introduction of a non-native species of crayfish, such as the red swamp crayfish.