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Dikerogammarus villosus (Sowinsky, 1894)

Common Name: Killer shrimp

Synonyms and Other Names:

Dikerogammarus villosus bispinosus Martynov, Gammarus villosus

S. Giesen, NOAA Great Lakes Environmental Research LaboratoryCopyright Info

Identification: Dikerogammarus villosus has a laterally compressed, curled, semi-transparent body consisting of a head (cephalon), thorax (pereon), and abdomen. Its head contains one pair of eyes, mouthparts (gnathopods) with relatively large and powerful mandibles, and two pairs of antennae. Its pereon consists of seven segments, each with a pair of walking legs (pereopods)—the first four pairs extending downward and forward and the last three pairs extending downward and backward. In females, extra branches that serve as space to shelter eggs are present on the walking legs. Its abdomen consists of six segments divided into two three-segment parts: pleosome (anterior) with brush-like limbs known as pleopods, and urosome (posterior) with shorter, immobile rod-like limbs called uropods. This species’ body coloration can range from transparent and striped to a uniform dark pigmented color; however, the most frequent coloration pattern is a light spot or stripe on each segment against a dark background (Devin et al. 2001, Nesemann et al. 1995). Newly released young resemble adults but are microscopic in size.

This species can be distinguished from other Dikerogammarus species by the high, conical protuberances on its urosomes. In larger males (> 16mm), these bumps are tipped with three to five spines. Moreover, the second antennae have a sparsely haired peduncle and a flagellum with dense ‘brush-like’ tufts of setae (MacNeil et al. 2010).

Size: Up to 30 mm (Nesemann et al. 1995). Males grow to be larger than females, and sexual maturity is reached at 6 mm in length (Devin et al. 2004).

Native Range: Ponto-Caspian basin.  Widely distributed in the lower reaches of the Danube River system in the region of Eastern Europe/Ukraine (Mordukhai-Boltowskoi 1969, Nesemann et al. 1995). Its original distribution was restricted to the lower Danube by the narrow valley of the Dunakanyar near the confluence of the Danube and Ipoly Rivers (Nesemann et al. 1995).

Ecology: Dikerogammarus villosus inhabits fresh/brackish water, lakes, rivers, and canals in areas with low current velocity (Devin and Beisel 2006). It can adapt to a wide variety of substrates as well as a wide range of temperature, salinity, and oxygen levels. This species attaches itself to fastened banks, sheet-pile walls, and surface algae mats and can inhabit any substrate except sand (Crosier and Malloy 2006, Devin and Beisel 2006). It can also anchor itself within deep rock pools and under porous stones (Nesemann et al. 1995). In the lower Rhine, this species reaches its highest densities on hard substrates, primarily boulders, rocks, and pebbles within 3 meters of the shoreline (Kelleher et al. 1998, Platvoet et al. 2009). Different size classes of individuals tend to separate spatially, with the smallest individuals typically found on roots or macrophytes and larger individuals found in cobble (Mayer et al. 2008). In river sections of high habitat complexity, D. villosus is able to coexist with other species of gammarids (Kley and Maier 2005).

This species is able to tolerate temperatures from 0-35°C, with an optimal temperature range of 5-15°C (Bruijs et al. 2001, Maazouzi et al. 2011, van der Velde et al. 2009, Wijnhoven et al. 2003). It naturally occurs at 17 ppt but can tolerate salinities ranging from 0 to 20 ppt (Bruijs et al. 2001, Grigorovich et al. 2003). While able to survive short exposure (3 hours) to full strength seawater, D. villosus experiences 100% mortality when exposed to 34 PSU (practical salinity units) for 24 hours (Santagata et al. 2008). The lethal minimum oxygen concentration for this species is 0.380 mg O2/L; while such conditions are considered hypoxic, other Ponto-Caspian amphipods invaders in the Baltic Sea can tolerate even lower oxygen concentrations (Dedyu 1980).

Dikerogammarus villosus is a omnivorous predator of many macroinvertebrates, including other gammarids, and is also able to collect detritus and to filter out suspended algae (Mayer et al. 2008). It exhibits a cannibalistic nature by occasionally eating conspecific newborns and weak adults (Devin and Beisel 2006, Dick and Platvoet 2000, Dick et al. 2002, Mordukhai-Boltovskoi 1949, Platvoet et al. 2009). Moreover, D. villosus has been observed to kill or injure potential prey without consuming it (Dick et al. 2002).

This amphipod is reproductive year round in its native range (Devin et al. 2004, Mordukhai-Boltovskoi 1949). Mean fecundity is around 30 eggs per female; however, females can to lay up to 194 eggs clutch, giving this species the highest fecundity of the European gammarids (Devin et al. 2004, Kley and Maier 2003, 2006, Pöckl 2007). In winter, when water temperatures drop to between 5.5 and 10.5°C, females exhibit a growth rate between 2.2 and 2.9 mm/month, while males show a slower growth rate of about 1.3 to 1.6 mm/month. With warmer spring water temperatures of 14.5-22°C, there is no significant difference in growth rate between the two sexes, and D. villosus is able to grow 2.6 mm in two weeks (Devin et al. 2004). Based on these observed growth rates, D. villosus may reach sexual maturity in as little as one month in 20°C waters (Devin et al. 2004). Well-established populations exhibit a female-biased sex ratio, with females making up about 60% of a mature population (Devin et al. 2004). Possible reasons for this skewed ratio include males’ larger body size, which makes them more prone to fish predation, and the presence of feminizing bacteria (Devin et al. 2004).

Means of Introduction: Dikerogammarus villosus has a moderate probability of introduction to the Great Lakes (Confidence level: High).

Potential pathway of introduction: Ballast (BOB) or no-ballast-on-board (NOBOB) water exchange/discharge

Dikerogammarus villosus is native to the Ponto-Caspian region, an invasion donor “hot spot”, and has expanded its range throughout Western Europe. Due to its high tolerance to varying levels of salinity, oxygen and temperature, D. villosus is considered a highly likely candidate for introduction to the Great Lakes through ballast water transport from European ships (Brujis et al. 2001, Dick and Platvoet 2001, Dick et al. 2002, Grigorovich et al. 2002, Maclsaac 1999, Mills et al. 1993, Ricciardi and Rasmussen 1998). As a benthic amphipod, ballast water flushing and/or exchange may be ineffective unless individuals are exposed to full-strength seawater for at least 24 hours (Santagata et al. 2008).

While there has been mention of hull fouling of ocean-going vessels as an alternate pathway of introduction (Devin and Beisel 2006), supporting evidence is unavailable at this time.


Not established in North America

Dikerogammarus villosus has a high probability for establishment if introduced to the Great Lakes (Confidence level: Moderate).

Dikerogammarus villosus has not yet been recorded in the Great Lakes, but this species has a history of successful invasions throughout Europe (Devin et al. 2001). In addition to a physiology that facilitates ballast water transport (relatively wide temperature and salinity tolerance), this species possesses many advantageous life history traits conducive to successful invasions, including: short generation time, rapid growth rate, female-biased sex ratio, early sexual maturity, high fecundity, brooding, production of multiple generations per year, exceptional predatory and competitive capabilities, ecological plasticity, and large size compared to related species (Bruijs et al. 2001, Devin and Beisel 2006, Devin et al. 2004, Dick and Platvoet 2000, bij de Vaate et al. 2002, Wijnhoven et al. 2003). These characteristics, combined with abundant potential food sources, make D. villosus a species expected to have high potential for spread if introduced to the Great Lakes ecosystem (Devin et al. 2003, 2004, Dick and Platvoet 2000, Dick et al. 2002, Grigorovich et al. 2003, MacIsaac et al. 2001, Ricciardi and Rasmussen 1998). Its propagule pressure during the shipping season (May-October) is likely to be high, as this period overlaps with D. villosus’ reproductive peak (May/June) (Pöckl 2009). Following introduction, this species is also likely to spread by hitchhiking on recreational gear, boats, or trailers, as was a probable vector for its introduction to Lake Garda, Italy (Casellato et al. 2005).

Climatic conditions (e.g., temperature, precipitation, seasonality) and abiotic factors (e.g., pollution, water temperature, salinity, pH, nutrient levels and current) relevant to the success of D. villosus in its native and introduced ranges are similar to those in the Great Lakes. One such adaptation enabling this species to overwinter is that its oxygen demand is greatly reduced at temperatures around 1°C (Wijnhoven et al. 2003).

A strong ecological connection exists between D. villosus and other Great Lakes invaders from the Ponto-Caspian, such as Dreissena polymorpha; under the theory of “invasional meltdown,” it has been predicted that invasion of the killer shrimp will be facilitated by these companion species (Devin et al. 2003, Dick and Platvoet 2000, 2002, Ricciardi and Rasmussen 1998). For instance, beds of D. polymorpha may facilitate establishment of this large amphipod by providing colonization substrate (Devin et al. 2003, Dick et al. 2002). Dikerogammarus villosus also exhibits variable morphology and coloration (Nesemann et al. 1995, Pjatakova and Tarasov 1996), which could facilitate its concealment and establishment in new environments.

Increased water temperature as a result of climate change is likely to enhance breeding, as has been observed with its relative D. haemobaphes (Kitisyna 1980). However, although D. villosus has broad environmental tolerances, particularly with respect to high salinity, it is not known to survive in waters warmer than 35°C and may not typically survive prolonged exposure to temperatures in excess of 27°C (Bruijs et al. 2001, Maazouzi et al. 2011, Van der Velde et al. 2009, Wijnhoven et al. 2003). This species prefers temperatures from 5 to 15°C and exhibits a limited potential to adjust to waters warmer than 20°C (Maazouzi et al. 2011).

The dispersal rate of this species across Europe is similar to that of many other Ponto-Caspian invasive amphipods (e.g., Dikerogammarus haemobaphes), spreading across the entire European continent in roughly 50 years (bij de Vaate et al. 2002).

Great Lakes Impacts: Dikerogammarus villosus has the potential for high environmental impact if introduced to the Great Lakes.

Native to the lower Danube river system and Caspian Sea basin, D. villosus has recently invaded and spread throughout most of Western Europe, causing significant ecological disruption. Dikerogammarus villosus is a fierce predator and superior competitor. Its ability to eat and displace other amphipods has led to the prediction of a great reduction in amphipod diversity if introduced to a variety of North American freshwater habitats (Dick and Platvoet 2000). In the Netherlands, D. villosus has replaced many populations of the European native amphipod species Gammarus duebeni, as well as those of the North American invader G. tigrinus (Dick and Platvoet 2000). Dikerogammarus villosus has displaced an additional Dikerogammarus invader (D. haemobaphes) in portions of the Danube and Rhine rivers (Mueller et al. 2002). This species also consumes eggs or juvenile stages of small fish, causing potential concern for game fish populations if introduced to the Great Lakes (Devin and Beisel 2006).

The short generation time, rapid growth rate, early sexual maturity, high fecundity, female-biased sex ratio, and large size of D. villosus as compared to related species make it a species expected to outcompete native species for resources (bij de Vaate et al. 2002). Dikerogammarus villosus also has been predicted to have serious direct and indirect negative environmental effects if introduced to the Great Lakes ecosystem (Dick et al. 2002).

Dikerogammarus villosus is host to several microsporidian parasites that may become emerging diseases in other crustaceans following host introduction (Bacela-Spychalska et al. 2012, Ovcharenko et al. 2010). Moreover, while many freshwater amphipods also serve as an intermediate host to acanthocephalan worms (parasites with birds and fish as final hosts), infection of D. villosus has not been confirmed (Médoc et al. 2006, in contrast to interpretation by Crosier et al. 2011 and others).

There is little or no evidence to support that Dikerogammarus villosus has the potential for significant socioeconomic impacts if introduced to the Great Lakes.

The socio-economic impact of this species on invaded areas of Western Europe is largely unknown. However, the ability of this species to consume eggs or juvenile stages of small fish creates a potential concern for fishery populations (Devin and Beisel 2006).

There is little or no evidence to support that Dikerogammarus villosus has the potential for significant beneficial effects if introduced to the Great Lakes.

Dikerogammarus villosus has displaced populations of other invading amphipods in Europe, including D. haemobaphes (another potential Great Lakes invader) (Mueller et al. 2002).


There are no known regulations for this species.

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

While no prevention mechanism exists for intracontinental dispersion, mandatory ballast control and ballast filtration systems are being implemented to prevent further transcontinental dispersion. Shoreline treatment plants for ballast water are also being considered, although this could be a costly option (Crosier et al. 2011).

While a specific method is unknown, it has been suggested that D. villosus can be killed by oxidizing biocides (Abdel-Fattah 2011).

Note: Check state/provincial and local regulations for the most up-to-date information regarding permits for physical and chemical control measures.

Remarks: Dikerogammarus bispinosus was originally described as a subspecies of D. villosus (Martynov 1925), but a more recent genetic study by Müller et al. (2002) demonstrated that these two taxa should be considered to be separate species.

Dikerogammarus villosus was collected beyond its native range in the Austrian waters of the Danube for the first time in 1989 (Nesemann et al. 1995). By 1992, this species was abundant in several sampled sites of the Bavarian Danube. It has since spread along the main Danube canal, entering the Main River in 1994 and successfully invading the Rhine River, where it was sampled in the Netherlands, in 1995 (Bij de Vaate and Klink 1995, Van der Velde et al. 2000). As of 1996, this species has been observed in almost all large rivers of Western Europe, as well as in the Baltic Sea basin (Bij de Vaate et al. 2002, Bollache et al. 2004). More recent observations in the Bug River (Konopacka 2004) and the Vistula River (Bacela et al. 2008), as well as reports from the U.K. (BBC 2011), demonstrate its continuing expansion.

Obesogammarus aralensis, listed by Grigorovich et al 2003 as having a high probability of invading the Great Lakes, is most likely a synonym for Dikerogammarus villosus



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Author: Dettloff K., G. Núñez, E. Baker, and A.J. Fusaro

Contributing Agencies:

Revision Date: 1/28/2015

Citation for this information:
Dikerogammarus villosusUSGS Nonindigenous Aquatic Species Database, Gainesville, FL, and NOAA Great Lakes Aquatic Nonindigenous Species Information System, Ann Arbor, MI.
<http://nas.er.usgs.gov/queries/greatlakes/FactSheet.aspx?SpeciesID=3&Potential=Y&Type=2&HUCNumber=> Revision Date: 1/28/2015

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.