Many spiders exhibit vivid colors that are not produced by pigments, but rather by optical interference, diffraction, and scattering — structural colors. Traditionally, structural color research in nature focused on birds, butterflies and beetles. But the long evolutionary history and extreme diversity of spiders provide fruitful new territory. The repeated evolution of blue in large, nearly blind tarantulas and the diversification of sexual display colors in tiny peacock spiders provide two striking examples. Here, we show how tarantula blue is produced using specialized hairs with complex hierarchical structure that greatly reduces iridescence — which has been a key obstacle to the production of synthetic structural colorants without the shimmering effects. On the other hand, the strikingly iridescent scales of the rainbow peacock spider (Maratus robinsoni) can produce every color of the rainbow, and may hold the secrets for future optical device miniaturization. We used an interdisciplinary biomimetic approach to investigate both questions by including techniques such as: morphological characterization (SEM/TEM), phylogenetic analysis, spectrophotometry, optical simulation, and rapid prototyping by 3D nano-printing. Particularly with the rapid prototyping capability, we can create engineering models to test biological hypotheses in a controlled manner that may not be feasible with the living systems. Hence, biomimicry is not only taking what we learned from natural systems to practical human applications, but it is also providing insightful feedbacks and ideas to deepen our understanding of the biological system subject matter during the process.