glowworm

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A bioluminescent larva or a wingless wormlike female of certain insects, especially fireflies and beetles of the family Phengodidae.

from The Century Dictionary.

• noun The common English name of Lampyris noctiluca, a species of pentamerous beetles, of the family Lampyridæ and subfamily Lampyrinæ: a name applicable strictly only to the female, which is wingless, somewhat resembles a caterpillar, and emits a shining green light from the end of the abdomen. The male is winged and not phosphorescent, resembling an ordiuary beetle; he flies about in the evening, and is attracted by the light of the female. The same name is given to other species of Lampyris, as L. splendidula. Some related beetles are known in the United States as fireflies and lightning-bugs.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Zoöl.) A coleopterous insect of the genus Lampyris; esp., the wingless females and larvæ of the two European species (L. noctiluca, and L. splendidula), which emit light from some of the abdominal segments.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun The larva or wingless grub-like female of a beetle from the families Phengodidae or Lampyridae that gives out a green light from its abdomen.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the luminous larva or wingless grub-like female of a firefly