I wasn't sure if the white zigzag that looks rather like dental floss was associated with the spider and its web, though it certainly seemed to be. This website has a lot of information about the Argiope spider, and (citing Behavioral Ecology magazine) explains the purpose of the zigzag material, known as stabilimenta:
Stabilimenta are conspicuous lines or spirals of silk, included by many diurnal spiders at the center of their otherwise cryptic webs. It has been shown spider webs using stabilimenta catch, on average, 34% fewer insects than those without. However, webs with the easily-visible markings are damaged far less frequently by birds flying through the web. It is an evolutionary tradeoff the spider can influence every time it builds a new web. The inclusion of stabilimenta is influenced by many factors, including prey density and web location.I thought that was fascinating. You can see more of the web in the photo below, from which the one above was cropped.