What is this strange worm-like creature?
I believe this is some sort of Cranefly larvae, see here:  I've found these guys both directly in streams and along the banks of rivers, but also underneath rocks far away from major sources of water. There are different types of cranefly larvae, but they all have the same characteristics, (bulbous bodies, worm like, not easily noticeable arms, alien encephilization)

It may also be deer fly larvae ( a type of horsefly ) but they typically are more &quot;spiky&quot; on the sides.