Spiders spin a variety of silk fibers and integrate them into webs with a wide range of architectures. Combined with clever behavioral strategies, these webs serve as effective prey capture devices. One of the most stereotypical and familiar web forms is the orb web, characterized by radiating lines of dry silk that support a sticky capture spiral. Dragline silk forms the attachment lines, perimeter frame lines, and radial scaffolding. These dragline threads are the most investigated spider silk fibers due to their strength and toughness. By comparison, the orb web’s adhesive capture threads have been largely ignored, which is rather surprising, as they hold insects in the web until a spider can subdue them. Here, we discuss two of the most prominent adhesive fibers produced by orb-weaving spiders – cribellar silk and viscid silk. We review the structure, chemistry, mechanics, and adhesive mechanisms of both these systems, to help in understanding how spider webs function in prey capture and to provide insights into designing novel adhesives.