Caterpillar or doodlebug (5)
I believe the answer is:
larva
'caterpillar or doodlebug' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for larva that I've seen before include "Tadpole or caterpillar, say" , "Grub, caterpillar stage" , "Insect in the first post-egg stage of its life" , "Maggots" , "Grub; insect" .)