Changes to spider distributions

Changes have undoubtedly occurred to habitats at an alarming rate especially in southern England, where modern agriculture and other developments have taken an enormous toll on wildlife habitats and their associated flora and fauna. However the level of spider recording on a detailed national basis is insufficient to adequately monitor quantitative changes in the populations of species. However, a few species have clearly increased their distribution, including Argiope bruennichi, a spider expanding its range in southern England as a result of climate change, in particular longer milder autumns. The crab spider Philodromus praedatus is a species with an interesting history in Britain. The spider is typically found on mature oak trees in open situations, in wood pasture, at the edge of woodland rides or in old hedgerows, but it is also sometimes found on other trees such as Field Maple. Although males are easy enough to distinguish by microscopical examination from other members of the aureolus group, females are difficult without dissection and reference to reliably identified specimens. It was first recorded from Dorset in the nineteenth century by Pickard-Cambridge (1879). In 1974 the species was still only known from old specimens taken at Bloxworth (Dorset), New Forest (Hampshire) and Shrewsbury (Shropshire). However, by the time Dr Peter Merrett published his review of nationally notable spiders in 1990 the spider had been recorded in ten counties mainly in southern England but also Inverness-shire, and the spider is now known from 25 counties. This remarkable change does not seem to be due to any increase in range or abundance, but rather the result of the recognition of good characters for its separation from other closely related species and a clarification of its ecological preferences.

New species to Britain continue to be discovered, such as Megalepthyphantes sp. nova from Sheppey and Wabasso replicatus from the Insh Marshes in 1999, Neriene emphana from the Isle of Wight in 2000, Macaroeris nidicolens from Mile End in East London in 2002 and one species, a six or eight eyed oonopid belonging to Orchestina or a closely related and possibly new genus, is still only known from six specimens collected by Ray Ruffell north of Colchester between 1992 and 1994. However the rate of discovery since the early 1950s has remained almost constant at an average of about 1.5 species per year (Merrett & Murphy, 2000).