The pterostigma is the somewhat triangular apical part of cell sc, between the apical bend of vein Sc, the costa, and vein R₁. It is often more opaque than surrounding membranous areas of the wing. The length of the pterostigma is measured from the level of the apex of vein Sc to the level of the apex of vein R₁. Its width is measured from the costa to vein R₁ at its greatest dimension. The pterostigma ratio is its length divided by its width.