Coursair
Aquarium Advice Addict
If you keep it, put it in a separate tank with a net over it. They are Predators and will go after your fish when they get big enough !!
I was getting my 10 gallon fish less tank ready to be used as a QT tank and found a dragonfly larva in it too. That makes two I have found in tanks with nothing new added in a month. I relocated the other one back outside. I may let this one grow to maturity in the Ten gallon. I am planning on QT'ing 5 black khuli loaches so they should be alright. I am going to feed it dried shrimp and blood worms. They eat other insects so it should do good. I have seen plenty of dragonfly larva in my pond but have never seen one transform to an adult.
Oh joy. Another thing to add to the nightmare list. 0_o. Good to know, however.
Dragonfly larvae cannot eat anything bigger than they are. The average size of a dragonfly larvae is around 1/2 inch. In the wild they eat tadpoles, water bugs, and mosquito larvae. A small tetra or similar size fish may be at risk but not much else. Fish in fact will eat them. Here is an interesting study done by a group of scientist that shows dragonfly larvae will die around fish from stress.
Dragonflies Are Literally Scared to Death of Fish | Insects, Larvae, Fish & Fear | Fear & Survivial | LiveScience
Return it to the wild if you can. Any still body of water would do. They are way more beneficial than they are a threat.