Silk fibers produced by the orb spiders Argiope amoena and Nephila clavata were examined using scanning electron microscopy. The fibers were produced on a horizontal surface by unanesthetized spiders. The fibers have different morphologies, physical structures, and fibrous compositions broadly consisting of one to four filaments and numerous fibrilliform filaments with varying diameters. The fibers are composed of a wide range of different silk fibrils (e. g. major and minor ampullate or other gland silk). We examined a range of silks produced by orb spiders. The spiders produce different silks for purposes such as web mooring, web radial threads, scaffolding anchoring silk of egg cases. In addition fiber deposited when moving towards prey enmeshed in the web, fiber deposited when returning to the web center, and fiber used to hang vertically downwards from a branch are all different. The studies indicate that these two species of orb spider can spin fibers of diverse complex structures constructed from fibrils from different glands that vary in number, diameter, morphology, and conformation depending on application. We interpret the variation in the silk produced by relating it to the required tensile properties, a biological cost–benefit principle, and the functional requirements for different natural environments and applications.