any of a number of beetles or beetle larvae that give off a luminescent light; esp., the wingless female or the larva of the firefly
See glowworm in American Heritage Dictionary 4
(glōˈwûrmˌ)
noun
Any of various luminous female beetles or beetle larvae of the families Phengodidae and Lampyridae, especially the larva or wingless grublike female of a firefly.