Tail close-up.
It uses the tail as an important part of its locomotion.
It seems to have a powerful hind foot, somewhat like a caterpillar.

The second to the last segment appears to be somewhat different from the other segments.
Could it be a light organ (?).
Or may just extra muscle and flexibility for locomotion (?).

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After reading Carmen's note, I decided to return to the Hackberry tree the next day (2/8/09).
There was a firefly larva wandering about within a foot or two of the one in the first image.
I was able to get shots of the head and tail.

I will include two more images of this individual - a close-up of the head and a close-up of the tail.