Rosser's Sac Spider

This project will help to conserve one of the UK’s rarest and most elusive spiders, known from only two sites in the Cambridgeshire Fens.

Rosser’s sac-spider (Clubiona rosserae) has historically been known from only 2 sites in the UK, both in the Cambridgeshire Fens. However its current population size in the UK is unknown. It is listed as a Priority Species by the UK Biodiversity Action Plan, and conservation action is ongoing.

Project Aims 
To secure Rosser’s sac-spider from extinction in East Anglia and the UK, and improve the management of fenland habitats for spiders in general.

What is Buglife doing?
Buglife is chairing the steering group and managing the field worker who is studying Rosser’s sac-spider and surveying current and potential sites. Anglian Water is sponsoring the work on the spider. English Nature is providing additional financial support and is planning to support a University of East Anglia PhD student who will study spider ecology. The British Arachnological Society is providing volunteer specialists and spider expertise.

At the end of the project we should know exactly where the spider occurs in England, its ecological requirements and whether more action is required to prevent the species becoming extinct in the UK. In addition, we will learn more about fenland management for spiders and this will be made available to landowners.

Project Update

In September 2010 Ian Dawson of the British Arachnological Society found a female in a pile of cut vegetation very close to where the species was seen in the early 1990s.This is the first record from the UK for 10 years and the first record from Chippenham Fen for 14 years. A Buglife survey of Lakenheath Fen RSPB reserve this year failed to relocate that population.

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