We report the investigation of a nano-scale antireflection structure in the black scales of the Troides aeacus butterfly wing, which can be viewed as a natural solar collector. The intelligence of light capturing hides itself in the intricate architectures aside from melanin effect. Reflection and transmission spectra of scales were obtained experimentally as well as with 3D FDTD (three dimensional finite difference time domain) method. Poynting vector maps which show the energy distribution of reflection and transmission in the micro geometric structure were portrayed as well. We demonstrated that the structure related antireflection behaviour is derived from the coupling effect of two main subunits of the hierarchical architecture, which are periodically aligned inverse-V type ridges and sub-wavelength nano-hole arrays.