Dikerogammarus villosus: The ‘Killer Shrimp’

Dikerogammarus villosus (Killer Shrimp)Dikerogammarus villosus (‘Killer Shrimp’). Click to enlarge.

Following the news and confirmed sighting of the aptly named ‘Killer Shrimp’ (Dikerogammarus villosus) by the Environment Agency in two sites in Wales (described by the EA as ‘particularly vicious and destructive’), both the EA and DEFRA are urging ALL to be vigilant when out fishing, walking along a body of water, etc.

Dikerogammarus villosus poses huge risks to our waters here in Wales (and anywhere else for that matter) due to it’s appetite for native species such as shrimp, young fish and insect larvae and is able, therefore, to alter the ecology of the habitats it invades.

Advice from the Welsh Assembly indicates that “anyone who uses these waters must take steps to prevent the species from spreading. Simple things like cleaning and drying equipment thoroughly after use and checking equipment when leaving the water are vital.”

Below you will find downloadable files detailing both the findings of the Cardiff Harbour Authority and also an informative flyer issues by the GB Non-Native Species Secretariat. We have also outlined how you can help us protect our rivers, lakes, reservoirs, and ponds as well as detailing the huge issues which this species of shrimp poses to them.


  • Dikerogammarus villosus is approximately 30mm long, much larger than our native freshwater shrimp.
  • Often has striped or spotted markings.
  • Mandibles are relatively large.
  • Behaviour is particularly vicious and destructive.

Behaviour & Characteristics

  • Kills its prey by biting and shredding them.
  • Much more deadly predator than native amphipods (partially due to its much larger and more powerful mouthparts).
  • Attacks and eliminates other gammarid species.
  • Colonises a wide variety of substrates, is capable of adapting to a wide range of habitats, and is able to survive fluctuations in temperature, salinity, and oxygen levels.
  • Sexual maturity reached at 6 mm in length.
  • Populations are predominantly female.
  • Exceptionally high growth rates (e.g., 1.3–2.9 mm per month during the winter and 2.0–2.6 mm over a two week period in spring).
  • Reproduce sexually, high fecundit- Reproduction occurs year round.
  • During mating, male carries smaller female on his back (i.e., amplexus).
  • Female can carry approximately 50 fertilized eggs and releases them into the ventral brood chamber, where they are incubated and develop.
  • Interactions between D. villosus and native gammarid species can result in displacement or local extinction of native species, thereby reducing biodiversity.
  • D. villosus has been observed attacking small fish, which raises concern over whether vulnerable life stages (eggs, larvae, and juveniles) of vertebrates may also be at risk.
  • May be an intermediate host of acanthocephalan worms (a parasite of birds and fish).


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