Industrial melanism in spiders: a reappraisal.

One consequence of the Industrial Revolution, which began in the mid-1700s in Britain, was to darken the surfaces of buildings and trees upon which many invertebrates rest and forage during the daytime. This led to the micro-evolution of darker forms of such species, which were better camouflaged from predators on these novel backgrounds--a phenomenon known as industrial melanism. This process has been particularly well studied in moths. In the 1960s, three short papers were published purporting to demonstrate the evolution of industrial melanism in spiders. Here, I reappraise these possible examples and, for the first time, compare images of typical and melanic forms from museum collections. The conclusion reached is that a population of the Zebra Spider Salticus scenicus in Stockport, Cheshire, was highly likely to have exhibited true industrial melanism. The linyphiid Drapetisca socialis, living on Beech trunks, also in Cheshire, may have shown the phenomenon but the lycosid Arctosa perita, from colliery spoil heaps in the English Midlands, probably did not. [ABSTRACT FROM AUTHOR]