Invertebrates are generally inconspicuous but they dominate biodiversity in Wales, as elsewhere. In Welsh terrestrial and freshwater environments there are probably more than 20,000 different species of macro-invertebrates and, as an example of their abundance, it has been estimated that there are more spiders in a three-hectare field than there are sheep in Wales. Invertebrates occupy all possible habitats from crevices in inter-tidal rocks to scree on the summits of our mountain tops, from birds’ nests to saturated moss at the edge of waterfalls. This extraordinary diversity is possible because of the specialised niches that many species inhabit as a result of their adaptations to specific environmental conditions. They are also crucially important to the health of ecosystems. From the earthworms that aerate our soil, to the bees that pollinate our crops, the woodlice that break down decaying plant material, the mussels that filter our river water, and the ladybirds that eat pest aphids, we rely on invertebrates for the basic resources we depend upon.
Invertebrates pose unique problems for conservation because of a combination of factors that together make many of our species vulnerable to change. Foremost amongst these is the annual life cycle that is characteristic of the vast majority of invertebrates, requiring that suitable conditions for breeding are present at the right time and in the right place each year. Most invertebrates lack the longevity of plants and vertebrates that allows them several attempts to reproduce. The small size of most invertebrates allows them to occupy micro-habitats - entire populations can be contained within small areas. This makes them particularly vulnerable if important small-scale features are inappropriately managed. Invertebrates are often highly sensitive to micro-climate and hence vegetation structure. Different life-stages often require different developmental conditions, making the presence of ecotones and juxtaposition of habitat mosaics especially important. Many species have poor dispersal ability and hence management must ensure that breeding habitat is within colonisation range at all times. Some species, such as those of pioneer habitats, are adapted for dispersal and will colonise new patches at some distance from their natal sites, but will require frequent (usually annual) management to create new patches. Others exhibit metapopulation dynamics and require patches of suitable habitat to be distributed at landscape scale.
Arachnida (spiders etc.) c550 species
Crustacea (woodlice, water fleas, etc.) c250 species
Mollusca (snails, slugs, etc.) c170 species
Coleoptera (beetles) c3000 species
Diptera (flies) c4000 species
Hymenoptera [excluding parasitic wasps] (bees, wasps, sawflies) c750 species
Hemiptera (bugs, leafhoppers, aphids, etc.) c1200 species
Lepidoptera (butterflies, moths) c1800 species
Trichoptera (caddisflies) c160 species
Top image shows Cicindela maritima (dune tiger beetle) - a scarce inhabitant of foredunes in England and Wales, with several Welsh sites including Morfa Dyffryn and Whiteford supporting strong populations.
Bottom image shows Odontomyia hydroleon (Barred Green Colonel) - a rare soldier fly occurring in only two sites in the UK. The base-rich flushes at Banc y Mwldan SSSI in Ceredigion is the only location in Wales for this species.
Image © NRW /MJ Hammett)