I noticed a couple of little aquatic insects in my tank a few weeks ago, and managed to identify them as damselfly nymphs. I figured they were (mostly) harmless, and didn't worry about it. I'm glad I lived and let live because last night I got a nice treat and another reminder of how much more fun aquariums are when they more closely resemble actual aquatic ecosystems.
Over the course of about 3 hours, I had 4 damselfly nymphs emerge from their nymph stage onto some emergent driftwood. Then they flitted about my house. I'd have tried to shoo them out the door, but it's cold and I doubt they'd have survived long.
For fish, there's a small school (~15) of Espey's rasboras, and couple of rummynoses. There are also about ten amanos and a half-dozen CRS shrimp. I have not noticed any missing shrimp, but I have not seen any babies in the two months that the tank has been set up.
Today I was checking my Co2 diffuser and noticed this same little bug in my tank. Last month I purchased 4 different types of plants from Petco(all growing). Also purchased 3 leopard snails from LFS. So I am not sure where this little creature came from....but I know my wife is freaked out by it.
The adult damsels will make alittle slit in plant stems and lay eggs in them. The eggs can last a long time and hatch depending on time and temperature. When you have a couple dozen of these guys in a densly planted tank, they'll do a lot of damage, eating every baby shrimp they can. I had dragonfly larve in my first shrimp tank and even watched them team up to kill the larger shrimp.