Periods in which wandering ant makes no progress (9)
I believe the answer is:
stagnates
'makes no progress' is the definition.
'periods in which wandering ant' is the wordplay.
'periods' becomes 'stages' (e.g. many stages of development**).
'in which' is an insertion indicator.
'wandering' indicates an anagram.
'ant' with letters rearranged gives 'nat'.
'stages' going around 'nat' is 'STAGNATES'.
(Other definitions for stagnates that I've seen before include "Festers" , "doesn't develop" , "becomes inactive" .)