Firefly's effulgent larva (4-4)
I believe the answer is:
glow-worm
(Other definitions for glow-worm that I've seen before include "Beetle whose larva-like wingless females emit light" , "Beetle whose wingless females are partly luminous" , "Shining beetle" , "Kind of beetles that emit greenish light" , "Beetle whose female bears luminescent green organs" .)