No, this is not a small snake or a large worm, it is a moving mass of Fungus Gnat larvae (Sciaridae spp.)! A group of campers at my 2005 science camp found these migrating maggots crossing the road the day after a big rain. The cohesive mass moved as a group to take on the appearance of a larger organism as a method of protection. I was thrilled to learn that Fungus gnats are responsible for pollinating Jack-in-the-Pulpit flowers! Cool!
Gnats, other flies, beetles, bees, ants, and many other insects go through complete metamorphosis. "Meta" means change, "morpho" means shape. All insects start out their life in the egg stage. An insect that goes through complete metamorphosis hatches from the egg as a larva. The larva is the "eating, pooping, growing and molting" stage of the insect's life. Some insects gain several thousand times their hatching weight and grow greatly in length at this stage. After molting up to 5 times the larva goes through the next stage of major changes. The larva sheds its' skin and becomes a pupa, in butterflies this is a chrysalis, in a moth it is a cocoon. In the pupa stage the insect becomes a soupy mix of rearranging cells, in time a new mouth, a different body shape, internal organs and wings develop. Soon the adult emerges from the larval stage. Some adult insects live for a very short time, some have no mouth and don't eat. Only adult insects have wings and are able to breed.