There was a very large reduction in the size and distribution of the North Merseyside population during the 20th century – perhaps as much as 80%. The current estimate of the local population is 1,000 adults. These are all located in the Sefton Coast sand dunes and surrounding area and are spread over widely fragmented sites. The Sefton population is considered the rarest of three ‘geographical races’ in Britain. One population within the Sefton coast area appears to be genetically distinct from the others, due to isolation.