Caterpillar food? (4)
I believe the answer is:
grub
I believe this is a double definition.
'caterpillar' is the first definition.
(thesaurus)
'food' is the second definition.
(grub is a kind of food)
(Other definitions for grub that I've seen before include "Larva; dig shallowly" , "Caterpillar - food" , "Dig - maggot - food" , "Gentle, food" , "Dig (up); hack writers' Street" .)