Strange creatures in my settling tank

[Tom Hack]

Hello All,

I have these strange creature in my settling tank that I believe hitched a ride with the duck weed I collected from a local pond.  The are reproducing because I am finding more and they have moved from my duck weed tank into the settling tank. They tend to stay on the bottom but I have seen them swimming around. 

The Critters are about a 1/4" long.  I did find one today with an elongated abdomen that was about 1 inch long in total.  

Any information on these critters?  

Thanks,

Tom

[B. H.]

  Looks to me like a pretty gnarly dragonfly nymph. 

[Janet Little]

I also have them in my duckweed tank, I assumed they were born there and eggs were laid by some flying creature. They get quite large.

[Fishy McFisherson]

definitely looks like dragonfly larvae to me. Some species can be quite aggressive little hunters at this stage and will eat fry and other small fish, while others just bury themselves in the sediment. If they're in your settling tank, I wouldn't worry about them too much.

[Jon Parr]

If you don't haw small fingerlings, they are great. But let me tell you, they decimated my koi and Sac Perch fry this year. Good news is that the survivor fry got fat eating the nymphs later on.