They don't reproduce while in their aquatic stage, only once they go airborn. Neat critters, just as they are predatory on smaller fish, big fish love to eat them.
yea, probalby from the plants. You should wash the plants before you put them into the tank. I think you could use a really light bleach soltuion, but I'm not sure.
Dragonfly nymphs are most active at night; that’s the best time to check for them. During the day they try to remain concealed. Flip the tank light on after it’s been off for a few hours. If there’s any more you’ll usually see them dart back down toward the gravel bed.
If you’re seeing a 1cm long nymph than any other eggs would have hatched by now. Newborn nymphs are only a couple of mm long.
I had a damselfly larva (very similar) in my tank for a bit. They came in on some stem plants (along with a couple of killifish). The damselfly took up residence in my java moss eventually. I took him out, though, along with the leeches and isopods that had also decided to live in my java moss.