Grub said to come up hot! (5)

I believe the answer is:

larva

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'grub' is the definition.
(thesaurus)

I cannot understand how the rest of the clue works.

(Other definitions for larva that I've seen before include "Tadpole or caterpillar, say" , "Caterpillar perhaps" , "Immature stage of an insect" , "Maggots" , "Immature form of (insect) development" .)

I've seen this clue in the Evening Standard.

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