I am pretty sure it's dragonfly larvae.
We Found A Green Worm Like Thing With Pinchers, Which Lives In Water With Tadpoles, Makes A Screaming Noise, Has Insect Legs In The Front 1/4 Of Its Body. What Is This Thing?
A screaming noise huh? Hmm... A dragonfly larvae is a possibility. You should google it..
Wow I found a bunch of those to once It was like a gross version of a stick bug but water dwelling. I never found out what they were. Though I am pretty sure they are harmless enough. I was never bitten by one. (=