Harmful bugs essentially eroded rocks (4)
I believe the answer is:
gems
This clue might be a double definition.
'harmful bugs' is the first definition.
The answer and definition can be both man-made objects as well as being plural nouns.
Perhaps you can see a link between them that I can't see?
'essentially eroded rocks' is the second definition.
The definition and answer can be both things that one consumes for nourishment as well as being plural nouns.
Perhaps there's an association between them I don't understand?
Can you help me to learn more?
(Other definitions for gems that I've seen before include "Precious stones" , "Jewels" , "Valuable stones" .)