I use to raise a dragonfly larva in an aquarium (like the big one pictured). I had some small minnows 1-2 inch long about 30 of them and baby catfish..I only had 1 dragonfly larva. At the time I thought it ate worms and would give a worm a day. It was about an inch and a half long but I soon noticed my minnows disappearing every day. That son of gun ate 3-4 minnows a day! It was amazingly fast underwater, and expert at ambushing... it would strike/pounce on the minnow, latch on to it and eat it alive..its an amazing predator to watch... It didn't prefer the baby catfish but had a voracious appetite for minnows. I would suspect a bunch of those could do damage on any minnows populations less than 3 inches long... fatheads are a lot slower then the creek minnows I had in there..so I suspect you are keeping them fed..On the good side A single dragonfly can eat 30 to hundreds of mosquitoes per day.

And that big one you have in the picture..well I wouldn't put my finger in a aquarium with one of those in there....just sayin...

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