A pterostigma is a group of specialized cells in the outer wings of insects, which are often thickened or coloured, and thus stand out from other cells. It is particularly noticeable in dragonflies but presents also in other insect groups, such as snakeflies, hymenopterans, and megalopterans.

The pterostigma is a dark pigmented spot on the leading (front) edge of the wings of some species of insect. The spot is towards the wing tip and often stands out due to its coloration. Experiments have shown that the pterostigma, being heavier than surrounding areas of the wing, helps the insect when gliding. In particular, the pterostigma reduces vibrations within the wing. The pterostigma is present in the fore and hind wings of dragonflies and damselflies. Other insects have pterostigmas in their fore wings such as some Hymenoptera and Neuroptera.