From OSU
Michael, there are several species of glowworms and all are elongate but their light organs can be the size you describe. Others have much smaller glow organs. I'm still thinking that you may be seeing one of the small mushroom species that is bioluminescent. We have a couple of the species in Ohio that can produce the bluish-white glow and one is very small. Occasionally, the Jack-o-lantern mushroom glows, but it is more of an orange color! The pulsating brightness however is more typical of some of the glowworm species. In short, not sure what you were seeing!