Killer shrimp
Dikerogammarus villosus
Dikerogammarus villosus is a relatively large amphipod crustacean native to the Ponto-Caspian region that has successfully invaded many European freshwater systems. Known as the 'killer shrimp', it is highly aggressive and exerts significant predation pressure on native macroinvertebrates. It typically inhabits hard substrates in rivers, lakes, and canals, often leading to a dramatic decline in local biodiversity.
Details
Identification
Two cone-shaped humps on the urosome segments; body often features dark stripes or mottling; exceptionally large and powerful first gnathopods.
Social behavior
Often found in extremely high population densities; exhibits highly aggressive behavior towards other amphipod species.
Diet
Predatory omnivore; feeds on other amphipods, insect larvae, leeches, and occasionally small fish.
Hunting strategy
Active predator and ambush hunter, frequently killing prey items without consuming them entirely (excess killing).
Spawning substrate
Eggs are carried in the female's brood pouch; no external substrate required.
Overwintering
Overwinters as an adult or juvenile within the sediment or under stones.
Ecology
Ecological role
Acts as an invasive top predator that reshapes benthic community structures and displaces native species.
Natural predators
Fish (such as European perch, eel, and invasive gobies) as well as water birds.
Competitor species
Gammarus pulex, Gammarus roeselii, Echinogammarus ischnus.
Ecosystem service
No known positive ecosystem services; tends to degrade local biodiversity levels.
Threats
No significant threats; the species is extremely adaptable and has high dispersal potential.
Scientific profile
Profile
Distinguishing features
The most important feature is the presence of cone-shaped protrusions (humps) on the urosome segments, particularly on the first and second segments. Additionally, the gnathopods are very powerfully developed. The mandibular palp features dense setation. Unlike Gammarus species, it lacks the typical rows of spines on the urosome segments, which are replaced by the eponymous humps.
Diet
Other amphipods, mayfly larvae, chironomid larvae, fish eggs, and small fish larvae; also consumes detritus and algae.
Reproduction
Sexual reproduction with a high reproductive rate. Females produce multiple clutches per year. Eggs are carried in the brood pouch (marsupium) until the young hatch (direct development).
Role in food web
Aggressive predator that displaces native species and massively alters the structure of the macrozoobenthos. Serves as food for predatory fish.
Protection & threats
Status not on standard scale
Main threats
None; the species itself is an invasive species that threatens native ecosystems.
Conservation measures
No conservation measures; focus is on monitoring and preventing further spread into previously uncolonized water systems.