The North American Eastern grey squirrel (Sciurus carolinensis) is a highly invasive mammalian species adversely affecting forest ecosystems worldwide, notably in Europe. The species extirpates sympatric red squirrel (Sciurus vulgaris) populations through resource competition and the spread of pathogenic squirrelpox virus (SQPV) infection. In the United Kingdom (UK), the Red Squirrels United (RSU) project empowered volunteers with the skills, equipment and protocols needed to undertake the proactive detection and subsequent removal of grey squirrels at local, regional and national scales as an aid to red squirrel conservation. The establishment of local volunteer groups to undertake this provided a strong post-project legacy where bespoke local management approaches reflected regional variation in woodland isolation and
invasion pathways. Here we highlight valuable lessons for international invasive species management via an adaptive volunteer-based approach to monitoring and control. This included the development of non-invasive techniques to determine the presence of pathological infections in wild squirrels, the provision of evolving approaches to grey squirrel control and where appropriate, red squirrel conservation translocation.