A silicon prismatic lens, whose shape is inspired by the apposition compound eyes of some dipterans, was investigated to improve the light-harvesting capability of silicon solar cells. The bioinspired compound lens (BCL) has a fractal construction procedure in which the cross-section of the lens is a frustum of a infinitely long circular cylinder at the zeroth-stage, and is decorated with sections of smaller cylinders at higher stages of construction. We found that the light-coupling efficiency of the best performing first-stage BCL cannot be enhanced by higher-order stages and is significantly superior to other kinds of textured surfaces. By coating the lens with a double layer anti-reflection coating further enhancement of efficiency can be obtained. Our strategy can also be adopted for solar cells not made of silicon.