This chapter involves those orders of invertebrates which are not insects – including crustaceans, spiders, myriapods and worms – which, though frequently overlooked, are useful indicators of the state of our wildlife, because of their profound response to environmental pressures.

The chapter is arranged in two broad sections – terrestrial and fresh water – but it will be seen that the pressures are common to both environments. Habitat destruction, climate change (with the secondary effects, such as drought, flood and changes in life cycle), changing agricultural practices and introduction of alien species have all played a part in forcing change in the British fauna, at broad scales, such as national distribution of species, and local scales, such as changes at a community or population level.

Among terrestrial invertebrates, colonists and introduced species tend to live mainly in gardens and other man-made habitats in southern or south-eastern England, where temperatures are higher, and competition may be reduced. In recent years, several of these species have begun to expand their range northward and westward, and at the same time to colonise semi-natural habitats.

Included in the case studies are examples of the contraction in distribution or population size of cold-loving species (e.g. highland flatworms, montane spiders) and the concomitant rise of those which prefer warmer climates (e.g. the colourful Wasp Spider, Argiope bruennichi), superimposed against the other pressures outlined above. […]