This is a dragonfly larva. Actually it is the shed exoskeleton of a dragonfly larva that just molted. They are very common in ponds and small lakes. This insect has made the news a lot lately because of all the trees it is killing in Florida. The drought has weakened the pine trees allowing the beetles to attack.
Healthy trees are usually strong enough to survive the beetles attack.
You can see in the picture how these insects can kill an entire pine forest. Da Bomb and Polly-themus both recognized these as ants. FloridaEnto also noticed the large chunks of leafs they are carrying and knew they must be leaf-cutter ants. Leaf cutter ants cut large portions of leaves off and carry the portion back to the nest. There it is composted and used to farm fungus that is then eaten by the ants.