Estimation of the web's capture thread length in orb-weaving spiders: Determining the most efficient formula

Orb-weaving spiders modulate their web-building behavior in response to cha nges in their situation (internal or external state), and this capacity is expected to directly influence fitness. To understand the rules underlying the investment devoted to web construction, we need to quantify precisely t he costs and benefits associated with web-building behavior. The sticky sil k (capture spiral) is costly to produce and set up and is a limiting factor in web building. Thus, it would be useful to have an efficient formula to calculate the total capture thread length (CTL) produced, which reflects th e investment devoted to foraging activities. On the basis of web photograph s we tested nine formulae on webs built by three species: Zugiella x-notata (Clerek), Arancus diadematus Clerck, and Larinioides sclopetarius (Clerek) . We compared the calculated lengths with lengths directly measured from ph otographs. We showed that the most efficient formula (CTLvh) species tested , together with its ease of use in the field, this formula represents a use ful tool for behavioral ecology studies on spiders.