Top view of two small red damselflies mating

A narrow scientific definition of a species is based on the ability to reproduce. For example, all dogs, no matter how different they look, can reproduce, as they are all the same single species. In the world of damselflies, reproduction happens by the famous locking method, which creates a heart-like shape when viewed from the side. However, for the many damselfly species to not confuse who to reproduce with, each damselfly species has a unique "lock", that will only fit members of the same species and opposite sex.