A larvas food (4)

I believe the answer is:

grub

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'food' is the definition.
(I know that food can be written as grub)

I don't understand how the rest of the clue works.

(Other definitions for grub that I've seen before include "Worm-like larva of an insect" , "Dig (up); hack writers' Street" , "Insect larva or slang food (4)" , "Nosh - larva" , "Beetle larva" .)

I've seen this clue in The Irish Independent.

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