A method for the quantitative evaluation of the production of spider-mite webbing or silk is described. It was employed to establish the pattern of silk secretion by Tetranychus cinnabarinus (Boisd.) at various combinations of temperature and relative humidity. All active mite stages spin webs, more silk always being produced at low humidities. Mites kept in continuous light secreted more silk than mites kept in continuous darkness or in alternating light and darkness. Leaf side had no effect on webbing quantity. The implications of these results for mite control, mate finding and migration are discussed.