I actually think dragonflies are pretty cool, and obviously they don't hurt people at all, but if they did . . .
|The Devil's Darning Needle (Image Source: Wikimedia Commons)|
A devil's darning needle looks similar to a dragonfly except that when it flies it always flies "backwards". They are encountered alone, in pairs, or in swarms of 2d20, and are a favorite summon of Beelzebub and his ilk when enforcing contracts. The darning needle attacks by poking, prodding, and piercing its prey, weaving it with invisible magic cords while it does. Eventually the prey is immobilized, at which point the darning needles wait for it to die before feeding on the carrion.
For statistics, use a sprite, except that its type is magical beast and every hit deals an additional 1 point Dex damage and they generally have 1 hp.