Pterostigma

It is particularly noticeable in dragonflies, but present also in other insect groups, such as snakeflies, hymenopterans, and megalopterans.

Without the pterostigmata, self-exciting vibrations known as flutter would set in on the wing above a certain critical speed, making gliding impossible.

Tests show that with the pterostigmata, the critical gliding speed is increased 10–25% on one species of dragonfly.

[2] Some female damselflies in the family Calopterygidae possess a pseudopterostigma.

This is similar in location on the wing to a true pterostigma but is crossed by veins and is only defined by its paler colour compared to surrounding areas of the wing.