I'm not sure how these get into tanks initially but the adult insects look like very small dragonflies. They both have an extendable lover jaw (labium) which they use to snag insects, worms, and possibly small fish. When ready to molt, they climb out of the water and out comes a damselfly. If you have large characins or bigger, you are fine. Anything smaller that a guppy is at risk. If you don't want an insect flying around your house or your fish getting eaten, I would remove it. Do not release as it may have bacteria that are not native to your waterways.