Spideis of similar miss but of two different species Araneus diadematus Cl. and Argiope aurantia L., build webs which have similar geometric patterns, but which differ in relative proportions and thread number. Within species, webs may also differreliably, presumably on a genetic basis. Fine detail of the web undergoes change throughout the lifetime of the spider, different for male and female; these changes are not simply response to the growing weight of the spider. Relatively simple restraints, such as availability of material for thread, result in adaptations of web-building which may at first appear to be based upon building experience, but which are in fact independent of it.