The killer shrimp (Dikerogammarus villosus) is listed as one of Europe’s 100 ‘worst’ invasive species. Native to the Ponto-Caspian region, killer shrimp rapidly spread to Western Europe transported in ship ballast water and was first discovered in the UK in 2010.
Despite its diminutive size, the killer shrimp is an aggressive predator with large powerful mandibles that it uses to kill its prey, by biting and shredding them. But its aggressive nature is not its only competitive advantage; the killer shrimp has a strange but clever adaptive behaviour. It has been known to attack and kill macro invertebrates but not eat them. Scientists believe this is a method of removing its competitors for resources.
Studies, both in the UK and in Western Europe, have revealed the killer shrimp’s competitive and adaptive nature can cause serious changes in aquatic communities due to the delicate ecological balance within aquatic ecosystems. More recently, concerns over the economic impact on fish stocks have arisen as the killer shrimp will attack and devour fish larvae and fish in the early stages of their life cycle.
The killer shrimp are also keen hitch hikers! They have been spread throughout the UK unknowingly on angling equipment, boats and waders. The Check, Clean, Dry campaign aims to prevent further dispersal by educating anglers and other water users on how to identify killer shrimp, and other invasive species, and to check for any of these known hitch hikers and report them if any are found.
The key identification features for the killer shrimp are the presence of two cone shaped protrusions on the tail topped with spines and the large powerful mandibles. Whilst they can grow up to 30mm, the killer shrimp are usually between 10-20mm long.
Berezina, N.A., Duris, Z. (2008) First record of the invasive species Dikerogammarus villosus (Crustacea: Amphipoda) in the Vlatava River (Czech Republic), Aquatic Invasions, 3, 455-460.
Dick, J.T.A., Platvoet, D., Kelly, D.W. (2002) Predatory impact of the freshwater invader Dikerogammarus villosus (Crustacea : Amphipoda). Canadian Journal of Fisheries and Aquatic Sciences, 59, 1078-108.
Photo Credits: Killer Shrimp (both Environment Agency)