Answer:

glowworm

Answer	Crossword Clue
GLOWWORM	Bioluminescent larva
GLOWWORM	Mills Brothers tune
GLOWWORM	Mills Brothers song subject

GLOWWORM	Firefly
GLOWWORM	Firefly's young
GLOWWORM	Firefly larva

Crossword

a puzzle consisting of a grid of squares and blanks into which words crossing vertically and horizontally are written according to clues.