Form of insect right inside rock (5)
I believe the answer is:
larva
This clue could be a double definition.
'form of insect' is the first definition.
(I've seen this before)
'right inside rock' is the second definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
Can you help me to learn more?
(Other definitions for larva that I've seen before include "Immature form of (insect) development" , "Grub; insect" , "Wriggler" , "Volcanic outpouring" , "Insect in the first post-egg stage of its life" .)