STICKY NOTE

As it's Halloween today I thought I'd share this slightly scary (for some people anyway) image of a Garden Spider that was expertly constructing a web outside my window last weekend.  Apparently spiders don't stick to their webs because they have separate spinnerets to produce sticky and non-sticky types of silk and are careful to travel along only the non-sticky portions.  I discovered this information on the web, appropriately enough, along with this one's scientific name (Araneus diadematus), and the fact that the spaces between each spiral and the next are proportional to the distance from the tip of a spider's back legs to its spinnerets.  But how do spiders know?