Itty-bitty bug (4)
I believe the answer is:
mite
'itty-bitty bug' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for mite that I've seen before include "Tiny creature found in food" , "Tiny arachnid, person or amount of money" , "Microscopic animal" , "Old piece" , "The widow's small donation" .)