I blew up your pics on photoshop but they only became blurry. Firstly they seem to look like miniscule prawns. But I've seen things like that under damp/wet rotting vegetation. Not swimming freely in water. On the ground they hop around like very large fleas. (Don't jump anywhere near as high though.) That's about the limit of my experience/observations. Maybe in Mexico they are something that looks similar but is totally different. One of our local fish would make short work of them, the Spangled Grunter. They eat every thing in with them. A small turtle would probably clean them up as well.
