The remarkable mechanical properties of spider silk, especially its extensibility and strength, have long fascinated naturalists and engineers alike. Recent advancements have focused on unravelling the structural hierarchies and biochemical compositions that confer these unique properties, paving the way for biomimetic applications in materials science and engineering. In this scenario, spider capture threads pose a unique challenge, as many spiders produce metastructures, which unknown properties depend on both the mechanical characteristics of the fibres composing them, and their geometrical arrangement. In this work, we focused on the biomechanics of the capture threads of the Southern house spider (Kukulcania hibernalis) employing a combination of high-resolution tensile testing, microscopic examinations, and theoretical modelling. Our findings reveal the critical role of the hidden lengths provided by a unique hierarchical looped fibre architecture, which enhance the thread’s extensibility. Thanks to the theoretical modelling, we reveal how the outstanding extensibility observed in the capture threads of Kukulcania can be explained independent of the nano-structure of the fibres. Furthermore, our research highlights the potential of spider silk meta-structures as a model system for developing fibre-based materials that mimic biological structures for enhanced mechanical performance.