Evil monsters (Damselfly larva) in fish tank

I just found a dead barb in one of my tanks... being nibbled on by this 6 legged velociraptor monster evil spawn from the blackness of death. A quick image search pointed me to Damselfly larvae...

This is the closest image I found of what the fuel of nightmares I found in the tank looked like
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So my question is... Have you guys ever dealt with these evil harbingers of death? Any ideas where they could come from (I don't have damselfly flying around the house ) What kind of impact could they have on the fish tank water? Could they possibly kill a full grown cherry barb or might there have been another COD? Any links to reputable online info about them? I've been searching online but only found hearsay level info on them, and tons of general background on the adult insects.

Putting this in inverts+plants since
a. this guy probably came in with some plant over a month ago   
b. they ARE inverts... though I'm very inclined to call them a very large disease.  
Let me know if you guys think this thread should live over in diseases.

Wow thats what killed that barb.  
Well you still have other beautiful tanks. Jelly

Yes they will kill fish,
It definitely came in on a plant you got
They will not affect the water although I would recommend removing it so you don't loose any more fish.

I have had some nasty dragonfly larva before that have killed and ate a 3" goldfish.

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I used to do a lot of benthic studies and research in college for UW and WA fish & game and came to know all these nasty little buggers all to well.

Yeah... I didn't take any pictures of this thing... I pulled it out of the tank and jumped on it and squished it and ran around screaming like a little girl at a justin beaver private concert before I could do anything intelligent like wonder what it was. This is the second time I run into one of these guys, so at least now I know what to watch out for. Thanks!

W T _?! Never seen anything like that in the years I've been in the hobby. That's horribly wicked.

Hey now...as 25yr flyfisherman I can tell you they get eatin by a LOT of trout and lead to some of the best Dry Fly experiences of the year!!!

TFP

These things can be a real problem in ponds when I'm spawning fish outside They can also just come in your tanks from one flying in during the summer time etc and laying eggs.

Both times I've caught them (I had one last November), it was because they had just killed some fish... so I'll totally vouch for them being nasty little buggers. Gotta watch out for them.

Fishy tank monsters...yuck! But I love your description of the "death scene"...   

I'd hate to see one of these in my tanks, and now I'm frightened to even try spawning fish outdoors. One of those things could eat an entire stock of white cloud minnows in a heartbeat. It would be a massacre! 0_0

MRTom wrote:6 legged velociraptor monster evil spawn from the blackness of death.

Now that's a description  

Missgrumpygills wrote:

MRTom wrote:6 legged velociraptor monster evil spawn from the blackness of death.

Now that's a description  

I don't think I did them justice either They move around like the aliens from Aliens... tails whipping around, big bug eyes staring, swimming around the tank faster than any fish... Pure evil!!! If they didn't grow up to leave the water and fly around the room, I'd love to keep a tank full of them!

TheFishPimp wrote:Hey now...as 25yr flyfisherman I can tell you they get eatin by a LOT of trout and lead to some of the best Dry Fly experiences of the year!!!

TFP

Trout LOVE these bad boys. My nymph box always has 2-3 damsel fly imitations in it.

I've had damsel fly larvae in my tanks before. The past few places I've lived have been near creeks or small ponds, so it's difficult to keep the adults from getting in the house.

I have witnessed them catch and kill an adult cherry shrimp. I have also seen my axolotl catch and eat an adult damsel fly that was trying to lay eggs. It's like "Wild Kingdom" up in my fish room!

For me, it was helpful to remove all of the wood from my tank and give it a quick rub with a wire brush. Once I found one damsel fly larvae, I quickly found several more. Well worth the effort!