AN alien creature responsible for causing immense economic and ecological damage has been spotted in a South Lakeland river estuary.

There have been two reports of the Chinese mitten crab being seen in the Duddon estuary near Millom.

Now scientists from a consortium of UK research institutes, including London's Natural History Museum, are calling on the help of “nature detectives” to discover to what extent the furry-clawed invader has gained a foothold.

The curious-looking crustacean features in the international list of the world’s 100 worst invasive species They are regarded as a pest because they damage fishing gear and unprotected river banks, block water systems and also compete with native species for food and habitat.

Rebecca Corrie-Close, co-ordinator of the Cumbria Freshwater Invasive Non-Native Species Initiative, said that the female crab can lay up to one million eggs. The two found at Millom had eggs and may have released them.

It is the young crabs that go up river and burrow into the banks.

“This causes erosion and the banks to collapse which leads to siltation of the river,” said Ms Corrie-Close. “This is bad for the river’s gravel beds which in turn is bad for the fish that spawn there.”

She said that if the mitten crab gains a foothold in an area then it is very difficult to remove them.

“There are no mechanical means or biological management methods and you cannot go putting chemicals into rivers,” she said. “We need to raise awareness and get people trained up to identify them.”

To that end the initiative has organised some training days next month for staff from organisations like the Lake District National Park Authority and the National Trust. These will be opened up for volunteers to learn about invasive species that live in and around rivers.

Paul Clark, of the Crustacea Research Group based at the Natural History Museum, said it was “worrying” as mitten crabs could take hold in the Lake District.

“There is a very large population in the Thames and you can see signs of extensive burrowing,” said Mr Clark. “There is an island called Chiswick Eyot where the Environment Agency has measured that the banks have gone back by six metres.”

Records show that mitten crabs have established populations in the Thames, Medway, Ouse Washes, Humber and the Dee Estuary. But there are a number of areas where the Natural History Museum’s records are incomplete.

Anglers, waterway workers, boating enthusiasts and other nature lovers can use an online survey, to identify and record any sightings of the alien species.

Sightings can be reported by phone (0191-222-5345), email or online and photographs can be uploaded by visiting www.mittencrabs.org.uk.

For more information about mitten crabs and the survey visit http://www.nhm.ac.uk/research-curation/research/groups/mitten-crab/ and www.marlin.ac.uk/marine_aliens