Invasive non-native species pose a very serious threat to native plants and animals throughout Great Britain, and have been identified as the second biggest threat to biodiversity worldwide. Many species have been introduced into England from other parts of the world. They include some of our most widespread and familiar plants and animals, such as sycamore, rhododendron, grey squirrel, pheasant and Canada goose. In urban situations, these may offer people valuable contact with nature, as with buddleia which is welcomed as a shrub with colourful flowers providing nectar attractive to native butterflies. These introduced species now form part of England’s biodiversity and have spread into our most isolated areas, so that there is unlikely to be a single SSSI without at least one.