Orconectes rusticus Girard, 1852

This species is native to areas of Michigan, Indiana, Ohio, Kentucky, and Ontario, and has been introduced widely north and east of this range (Taylor et al. 1996). In Wisconsin, O. rusticus has displaced its native congener O. virilis (Hagen) and the previously introduced O. propinquus (Girard) from lakes and streams (Capelli and Munjal 1982, Lodge et al. 1986) as a result of its aggressive behavior (Capelli and Munjal 1982), rapid growth (Hill et al. 1993), high population densities (≥ 21/m2 ; Charlebois and Lamberti 1996, Lodge and Hill 1994, Momot et al. 1978), and reproductive interference with native species (Garvey and Stein 1993, Lodge et al. 2000, Perry et al. 2002). (Klocker and Strayer, 2004)

Orconectes rusticus was clearly dominant over O. limosus....Both species of crayfish readily ate native bivalves. Crayfish preferred small bivalves and those not buried in sediment. Both species consumed approximately the same number of clams (O. limosus ate 25.0% and O. rusticus ate 27.9% of clams offered) and approximately the same size of clams (average clam size eaten: O. limosus = 5.07 mm and O. rusticus = 4.84 mm)..... (Klocker and Strayer, 2004)

O. rusticus aggressive nature, greater fitness, and large chelae and body size allow it to displace native crayfish from food and habitat (Byron & Wilson, 2001; Garvey et al, 2003; Garvey & Stein, 1993; Hill & Lodge, 1999; Klocker & Strayer, 2004). Displacement from food causes reduced fitness to its cogeners and displacement from habitat increases predation pressure (Hill & Lodge, 1994). O rusticus displaces native crayfish, O. virilis, and previous invader, O. propinquus, from lakes throughout northern Wisconsin (Byron & Wilson, 2001; Garvey & Stein, 1993; Hill & Lodge, 1994). Along with direct competition and displacement, research indicates that fish and other predators avoid O. rusticus because of its larger chelae and body size and this selective predation pressure is likely an important driver in the replacement of crayfish species by rusty crayfish (Roth & Kitchell, 2005; DiDonato & Lodge, 1999). O. rusticus is known to hybridize with native crayfish O. propinquus in Lake Michigan (Jonas et al, 2005). In northeastern United States, O. rusticus may pose a threat to native crayfish O. limosus, which it was found to dominate in shelter competition and aggression trials (Klocker & Strayer, 2004).

We suggest that O. rusticus poses a potential danger to native bivalve populations. Although both species of crayfish consumed approximately the same density and sizes of clams, O. rusticus can live at very high densities (18–21/m2, Charlebois and Lamberti 1996; 11.9/m2, Lodge et al. 1985; 34–82/m2, Lodge and Lorman 1987), with these densities often being larger in comparison to many of its congeners (Lodge et al. 1985, Momot et al. 1978). This subsequently has raised the number of crayfish in many of the waterways in which O. rusticus has successfully invaded (Daniels 1998, Hobbs et al 1989, Lodge and Lorman 1987). Therefore, the threat of increased predator populations can affect already threatened unionid populations. (Klocker and Strayer, 2004)

Reproductive interference (e.g., between nonindigenous signal crayfish and native noble crayfish in Sweden; Soderback 1995) and introgressive hybridization between nonindigenous and native crayfishes can add harm tothat caused by ecological displacement mechanisms (Perry et al. 2002). Mechanisms associated with the production of sterile or inviable offspring often play particularly important roles in the genetic decline of a species (Levin et al. 1996). Even when hybrids are fit and fertile, genetic swamping may still occur if the native population has already been reduced by competition, predation, or disease vectored by a nonindigenous species (Levin et al. 1996). For example, hybridization with Orconectes rusticus increased the displacement rate of O. propinquus by over 20% relative to that caused by ecological factors alone (Perry et al. 2001a). O. rusticus readily mates with O. propinquus to produce fertile offspring, with F1 hybrids able to outcompete both parental species for food and shelter (Perry et al. 2001b). Despite initial hybrid vigor (particularly in survivorship), further study showed that this vigor broke down in subsequent generations (W.L. Perry, T. Arcella, J.L. Feder, D.M. Lodge, unpublished data), thus leading to the lack of a stable hybrid zone and an increased rate of decline in O. propinquus populations. ) (Lodge et al., 2012)

The most visible impact of rusty crayfish in Trout Lake was a shift to lower macrophyte abundance and species richness. Negative effects of crayfish on macrophytes are well documented (Lodge and Lorman 1987; Hanson and Chambers 1995; Nyström and Strand 1996). In experimental work, rusty crayfish have reduced macrophyte abundance as a result of nonconsumptive destruction (Lodge et al. 1994). Crayfish may also cause damage while grazing on periphyton or physically uproot seedlings or established plants in the process of digging burrows or foraging. (Wilson et al. 2004)