Grub, eg (5)
I believe the answer is:
larva
'grub eg' is the definition.
(grub is a kind of larva)
This is the entire clue.
(Other definitions for larva that I've seen before include "immature six-footer?" , "E.g. caterpillar form" , "Volcanic outpouring" , "Tadpole or caterpillar, say" , "Caterpillar, for example" .)