The demon shrimp – scientific name Dikerogammarus haemobaphes – is a close relative of another invasive species that was identified in the UK two years earlier, Dikerogammarus villosus; also known as the “killer” shrimp.

Both shrimps are highly invasive and potentially very damaging to Britain’s native ecosystems. Although at about 18mm long the demon shrimp is smaller than its killer cousin, both tend to be larger than most native British shrimps.

The Environment Agency describes the killer shrimp as a “voracious predator” that preys on a range of native species including young fish and can significantly alter ecosystems. Since it was first identified in Cambridgeshire it has turned up in Norfolk, South Wales and in the Midlands, although efforts to restrict its further spread are currently having some success.

In 2012 when Grant first identified the demon shrimp in a water sample taken from the River Severn, he explained his concern that it too may spread to other waterways: “Unfortunately the River Severn links to the national canal network, which itself connects to many other major rivers.”

That concern appears to have been borne out, with the Environment Agency confirming that the species is widely distributed throughout the Midlands and south of England, to the extent that it may have been present for some time before first being identified. Unlike the killer shrimp, it appears still to be spreading, with records now from the north of England.Grant is a laboratory scientist working in APEM’s Manchester headquarters.

He discovered the demon shrimp in a sample he was analysing as part of a detailed study being carried out by Severn Trent Water.He said: “Identifying a new species is an exciting moment. But when I first saw a shrimp I didn’t recognise, it was also deeply worrying. “Exciting, because it’s interesting to identify a new or newly arrived species.

“Worrying, because I knew the damage this innocent looking little shrimp was likely to bring to our rivers and waterways.”

Like the killer shrimp, the demon shrimp originates from Eastern Europe and had been spreading steadily into the rivers of Western Europe for at least 20 years. Scientists had predicted that it would arrive in the UK sooner or later, so were on the look out for it.

Even so, it was very difficult to identify with certainty for the first time. Examining them under the microscope reveals several differences between the invasive and native species, but separating the killer from the demon shrimp is more challenging. Grant had to look for tell-tale features at the rear of its body, which help to distinguish between the two.

“We may never know how it got to the UK, but now that it is here the important thing is to try to stop it spreading. People can help by following the ‘check, clean, dry’ code for their boating and angling gear before using it at another location,” says Grant.

If anyone suspects they have seen a killer or demon shrimp, they should contact the national non-native species recording group at alert_nonnative@ceh.ac.uk.

Find out more about the check, clean, dry code, or for more information on invasive species in general visit the GB Non-native Species Secretariat.

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If you have any queries, please contact Dr Michael Dobson, associate director.
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