Why do orb-weaving spiders make webs with sticky spirals but non-sticky spokes?

Orb webs are engineered so that different parts do different jobs. The radial threads act as the framework and help the spider sense vibrations from prey, while the spiral threads are coated with sticky droplets that capture insects. This separation of function makes the web both strong and sensitive. The spider can move across the non-sticky spokes more easily than across the sticky spiral. The design is one of nature’s clearest examples of functional specialization in a trap.