Factors influencing the size of the orb web in Araneus diadematus

The size of the web built by Araneus diadematus is influenced by several factors. The single most important factor is of course the size of the spider, but other factors also play a role. One of these factors is the supply of silk in the glands of the spider. In this study, the influence of the supply of silk (deduced from the time since the spider had built its previous web) on the size of the web is quantitatively analysed. It was found that the time since the spider had built the previous web significantly influenced the size of the current web, but only if the current web was built within 20 hours after the previous one. INTRODUCTION Spiders build webs of varying sizes. The decision by the spider to build a web of a certain size is influenced by several factors (Tab. 1). Of these factors, the most important ones are certainly the species and the size of the spider. In an experiment designed to show the influence of silk supply on web size, Eberhard (1988) has shown that webs built during the day after the web the spider had built during the night had been destroyed by the experimenter were smaller than the ones built in the night. He concluded that the spiders were constrained by their silk supply when they built the second web. Similar observations have been made by Vollrath (1992). In our laboratory, I observed the construction of several webs built in a series by the same spider. I could show that the size of the web correlated with the time since this spider had built the previous web, as long as this time was less than 20 hours. No correlation could be found if the time since building the previous web was longer than 20 hours.