When both of these larva moved...there was a dark band within the bodies that moved forward to the head and then back again. It looks like it is somehow being propelled by something within it's body instead of by legs...however, it's not like a worm because I've never seen that flashing black movement on a worm. Do you know what I'm talking about?

inside this crane fly larva is actually the heart or ciculatory system of the larva. Insects have a open cirulatory system and the heart is positioned on the dorsal of the body cavity, quite opposite to our system. The hearts are quite visible in many of the pale green color caterpillars. - Chen

That's interesting.

There is nothing in my book that suggests anything that would give you an answer. I can make one suggestion but not having seen the phenomenon I will not claim that it is the answer.

For easy mobility in some groups you can see that larvae do not just use the consecutive shortening and lengthening of the body (I do not know what the correct word for that is, in bowels it is peristaltic movement) but sometimes they also use the mouth parts as a kind of anchor to pull themselves forward. Maybe what you did see was some movement of the pharyngeal complex during this pull-and-release exersise.

Paul

http://www.diptera.info

Well, it seems like this was a bit large to be a fungus gnat larva. I could be wrong, but I'm thinking it was over an inch long. Of course, I have no idea how large a fungus gnat larva is...but I'm guessing it would be somewhat relative to it's adult size?

Larvae of the larger fungus gnats, e.g., Keroplatus can easily reach about one inch, so i think we are safe here. In my experience you are left with little gnat when compared to the actual size the larva had.

Paul

http://www.diptera.info