Orb-weaving spiders must localize and size prey rapidly upon impact, despite their poor vision and small brains. Leading hypotheses suggest that the local material intelligence of orb web threads enables spiders to tune them individually to resolve prey location and mass cues by decoding vibrations across the spider’s eight independent legs—a task requiring high cognitive overhead if material intelligence is used alone due to the web’s inherent geometric and material irregularities. Here, we reveal that an orb web also exhibits a form of global mechanical intelligence: the spider’s entire body acts synergistically with the flexible web’s global vibration motion as a gyroscope and cue decoder. Through extensive simulations and experiments, we demonstrate that impact events trigger specific pitch-roll dynamics in the spider’s body, facilitated by the web architecture. These dynamics provide robust prey localization cues, without requiring processing of sensory input from eight individual legs; offloading some cognitive tasks onto the web. The findings reveal a novel source of information for spiders, and offer a blueprint for realizing transformative structures with cognitive functions.