''Dikerogammarus villosus'', also known as the killer shrimp, is a species of

amphipod Amphipoda () is an order of malacostracan crustaceans with no carapace and generally with laterally compressed bodies. Amphipods () range in size from and are mostly detritivores or scavengers. There are more than 10,700 amphipod species cur ...

crustacean Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...

native to the Ponto-Caspian region of eastern Europe, but which has become invasive across the western part of the continent. In the areas it has invaded, it lives in a wide range of habitats and will prey on many other animals. It is fast-growing, reaching sexual maturity in 4–8 weeks. As it has moved through Europe, it threatens other species and has already displaced both native amphipods and previous invaders.

Description

''D. villosus'' can grow up to in length, relatively large for a freshwater

. It varies in appearance, with some specimens being striped, and some not. It has relatively large

mandibles In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone i ...

which allow it to be an effective predator.

Distribution

''D. villosus'' was originally found in the lower courses of large rivers in the

Black Sea The Black Sea is a marginal sea, marginal Mediterranean sea (oceanography), mediterranean sea lying between Europe and Asia, east of the Balkans, south of the East European Plain, west of the Caucasus, and north of Anatolia. It is bound ...

and

Caspian Sea The Caspian Sea is the world's largest inland body of water, described as the List of lakes by area, world's largest lake and usually referred to as a full-fledged sea. An endorheic basin, it lies between Europe and Asia: east of the Caucasus, ...

drainage basin A drainage basin is an area of land in which all flowing surface water converges to a single point, such as a river mouth, or flows into another body of water, such as a lake or ocean. A basin is separated from adjacent basins by a perimeter, ...

s. It has become an

invasive species An invasive species is an introduced species that harms its new environment. Invasive species adversely affect habitats and bioregions, causing ecological, environmental, and/or economic damage. The term can also be used for native spec ...

across central and western Europe, using the

Danube The Danube ( ; see also #Names and etymology, other names) is the List of rivers of Europe#Longest rivers, second-longest river in Europe, after the Volga in Russia. It flows through Central and Southeastern Europe, from the Black Forest sou ...

river and its

tributaries A tributary, or an ''affluent'', is a stream or river that flows into a larger stream ('' main stem'' or ''"parent"''), river, or a lake. A tributary does not flow directly into a sea or ocean. Tributaries, and the main stem river into which the ...

in its expansion. It is thought to have first escaped from the Danube in 1992 when the

Rhine–Main–Danube Canal The Rhine–Main–Danube Canal ( German: ''Rhein-Main-Donau-Kanal''; also called Main-Danube Canal, RMD Canal or Europa Canal), is a canal in Bavaria, Germany. Connecting the Main and the Danube ri ...

was opened and has since spread to nearly all the major rivers in western Europe, including the

Rhône The Rhône ( , ; Occitan language, Occitan: ''Ròse''; Franco-Provençal, Arpitan: ''Rôno'') is a major river in France and Switzerland, rising in the Alps and flowing west and south through Lake Geneva and Southeastern France before dischargi ...

Loire The Loire ( , , ; ; ; ; ) is the longest river in France and the 171st longest in the world. With a length of , it drains , more than a fifth of France's land, while its average discharge is only half that of the Rhône. It rises in the so ...

Seine The Seine ( , ) is a river in northern France. Its drainage basin is in the Paris Basin (a geological relative lowland) covering most of northern France. It rises at Source-Seine, northwest of Dijon in northeastern France in the Langres plat ...

Moselle The Moselle ( , ; ; ) is a river that rises in the Vosges mountains and flows through north-eastern France and Luxembourg to western Germany. It is a bank (geography), left bank tributary of the Rhine, which it joins at Koblenz. A sm ...

Meuse The Meuse or Maas is a major European river, rising in France and flowing through Belgium and the Netherlands before draining into the North Sea from the Rhine–Meuse–Scheldt delta. It has a total length of . History From 1301, the upper ...

Rhine The Rhine ( ) is one of the List of rivers of Europe, major rivers in Europe. The river begins in the Swiss canton of Graubünden in the southeastern Swiss Alps. It forms part of the Swiss-Liechtenstein border, then part of the Austria–Swit ...

and

Main Main may refer to: Geography *Main River (disambiguation), multiple rivers with the same name *Ma'in, an ancient kingdom in modern-day Yemen * Main, Iran, a village in Fars Province *Spanish Main, the Caribbean coasts of mainland Spanish territ ...

, as well as the

Baltic Sea The Baltic Sea is an arm of the Atlantic Ocean that is enclosed by the countries of Denmark, Estonia, Finland, Germany, Latvia, Lithuania, Poland, Russia, Sweden, and the North European Plain, North and Central European Plain regions. It is the ...

. It is unknown how the species is dispersed but it is probably related to shipping activity. It spread quickly through western Europe; found in the Rhine at the German–Dutch border (1995), the canals and rivers of northern Germany (1998), the Baltic

Szczecin Lagoon Szczecin Lagoon (, ), also known as Oder Lagoon (), and Pomeranian Lagoon (), is a lagoon in the Oder estuary, shared by Germany and Poland. It is separated from the Pomeranian Bay of the Baltic Sea by the islands of Usedom and Wolin. The la ...

(2001), the Moselle (2001), the Netherlands (2002),

Lake Constance Lake Constance (, ) refers to three bodies of water on the Rhine at the northern foot of the Alps: Upper Lake Constance (''Obersee''), Lower Lake Constance (''Untersee''), and a connecting stretch of the Rhine, called the Seerhein (). These ...

(2003),

Lake Leman Lake Geneva is a deep lake on the north side of the Alps, shared between Switzerland and France. It is one of the largest lakes in Western Europe and the largest on the course of the Rhône. Sixty percent () of the lake belongs to Switzerl ...

, the Rhine in France (2003), the (2003) and

Lake Garda Lake Garda (, , or , ; ; ) is the largest lake in Italy. It is a popular holiday location in northern Italy, between Brescia and Milan to the west, and Verona and Venice to the east. The lake cuts into the edge of the Eastern Alps, Italian Alp ...

(2003). Its spread is thought to be related to the previous introduction of the

zebra mussel The zebra mussel (''Dreissena polymorpha'') is a small freshwater mussel, an Aquatic animal, aquatic bivalve mollusk in the family Dreissenidae. The species originates from the lakes of southern Russia and Ukraine, but has been accidentally Intro ...

, ''Dreissena polymorpha'' which it has evolved alongside. In September 2010, it was found in

Grafham Water Grafham Water is an biological Site of Special Scientific Interest (SSSI) north of Perry, Huntingdonshire. It was designated an SSSI in 1986. It is a reservoir with a circumference of about , is deep at maximum, and is the eighth largest rese ...

Cambridgeshire Cambridgeshire (abbreviated Cambs.) is a Ceremonial counties of England, ceremonial county in the East of England and East Anglia. It is bordered by Lincolnshire to the north, Norfolk to the north-east, Suffolk to the east, Essex and Hertfor ...

, the first report of the species in the

United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Northwestern Europe, off the coast of European mainland, the continental mainland. It comprises England, Scotlan ...

and it was found in Wales in November 2010. In March 2023, it was found in

Vättern Vättern ( , ) is the second-largest lake in Sweden, after Vänern, and the sixth-largest lake in Europe. It is a long, finger-shaped body of fresh water in south central Sweden, to the southeast of Vänern, pointing at the tip of Scandinavia. ...

Sweden Sweden, formally the Kingdom of Sweden, is a Nordic countries, Nordic country located on the Scandinavian Peninsula in Northern Europe. It borders Norway to the west and north, and Finland to the east. At , Sweden is the largest Nordic count ...

and it is the first time it is encountered in the northernmost part of Europe. There are fears that it could spread to the

Great Lakes The Great Lakes, also called the Great Lakes of North America, are a series of large interconnected freshwater lakes spanning the Canada–United States border. The five lakes are Lake Superior, Superior, Lake Michigan, Michigan, Lake Huron, H ...

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

in future, carried in the

ballast water Ballast is weight placed low in ships to lower their centre of gravity, which increases stability (more technically, to provide a righting moment (physics), moment to resist any Heeling (sailing), heeling moment on the Hull (watercraft), hull). I ...

of ships.

Ecology

In its natural range, ''D. villosus'' is not the most abundant species of amphipod and it does not behave as aggressively as it does in areas it has invaded.

Habitat

''D. villosus'' can colonise many types of

habitat In ecology, habitat refers to the array of resources, biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species' habitat can be seen as the physical manifestation of its ...

as it is able to tolerate a wide range of temperatures (), low oxygen concentrations, and

salinity Salinity () is the saltiness or amount of salt (chemistry), salt dissolved in a body of water, called saline water (see also soil salinity). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensio ...

up to 20

‰ The phrase per mille () indicates parts per thousand. The associated symbol is , similar to a per cent sign but with an extra zero in the divisor. Major dictionaries do not agree on the spelling, giving other options of per mil, per mill, pe ...

. It is found in lakes, canals and rivers living in a range of substrates. When found in

lotic River ecosystems are flowing waters that drain the landscape, and include the biotic (living) interactions amongst plants, animals and micro-organisms, as well as abiotic (nonliving) physical and chemical interactions of its many parts.Angelier ...

environments, the species prefers habitats with relatively mild currents. It is thought that zebra mussels change habitats by increasing the amount of benthic organic matter, which benefits ''D. villosus'' helping them to outcompete other species. When given a choice, ''D. villosus'' spend more time feeding around zebra mussel shells than a bare substrate.

Feeding

''D. villosus'' is

omnivorous An omnivore () is an animal that regularly consumes significant quantities of both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize ...

and feeds on a variety of

invertebrate Invertebrates are animals that neither develop nor retain a vertebral column (commonly known as a ''spine'' or ''backbone''), which evolved from the notochord. It is a paraphyletic grouping including all animals excluding the chordata, chordate s ...

s, including other members of the

Gammaridae Gammaridae is a family of amphipods. In North America they are included among the folk taxonomic category of " scuds", and otherwise gammarids is usually used as a common name. They have a wide distribution, centered on Eurasia, and are euryha ...

family. It has been found to kill

blue-tailed damselfly The blue-tailed damselfly or common bluetail (''Ischnura elegans'') is a damselfly, belonging to the family Coenagrionidae. Subspecies and varieties Subspecies and varieties include: *''Ischnura elegans ebneri'' Schmidt, 1938 *''Ischnura elegan ...

nymphs, water hoglice, water boatman, fish

leech Leeches are segmented parasitism, parasitic or Predation, predatory worms that comprise the Class (biology), subclass Hirudinea within the phylum Annelida. They are closely related to the Oligochaeta, oligochaetes, which include the earthwor ...

es as well as small fish and the eggs of other

vertebrate Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...

s. ''D. villosus'' sometimes kills prey but does not eat it; it kills its prey by biting it with its large mandibles and then shreds it before eating it. ''D. villosus'' also consumes many other forms of food, including grazing on biofilms, consuming plant detritus, eating and re-digesting feces, and feeding on organic matter and algae suspended in the water column.

Growth and reproduction

''D. villosus'' breeds all year round so long as the water temperature is above . When they mate, the female is carried on the ventral side of the male. Each pair produces an average of 27 eggs, but up to 50 eggs can be laid. The young animals become sexually mature in 4 to 8 weeks, once they are 6 mm in length and after

moulting In biology, moulting (British English), or molting (American English), also known as sloughing, shedding, or in many invertebrates, ecdysis, is a process by which an animal casts off parts of its body to serve some beneficial purpose, either at ...

several times. They are fast-growing, during winter increasing by 1.3–2.9 mm in length per month and by 2.0–2.6 mm every two weeks in spring. Populations are predominantly female.

Effects on other species

In the Netherlands, ''D. villosus'' is threatening the native amphipod species '' Gammarus duebeni'', as well as '' Gammarus tigrinus'' which had previously become invasive after previously being introduced from North America. It is thought to have displaced two other species of ''

Dikerogammarus ''Dikerogammarus'' is a genus of amphipod crustacean Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustac ...

'' (''D. bispinosus'' and ''D. haemobaphes'') which were previously invasive in the Danube. Its ability to attack and feed on a range of species could cause the local

extinction Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

of some species.

References

External links

Species Profile - Killer Shrimp (''Dikerogammarus villosus'')
National Invasive Species Information Center,

United States National Agricultural Library The United States National Agricultural Library (NAL) is one of the world's largest agricultural research libraries, and serves as a national library of the United States and as the library of the United States Department of Agriculture. Locate ...

.
Invasive Species Compendium
CAB International {{Taxonbar, from=Q447913 Gammaridae Crustaceans described in 1894