Terrified picnicker's ant problem (5-8)
I believe the answer is:
panic-stricken
'terrified' is the definition.
(I know that terrified can be written as panic-stricken)
'picnicker's ant problem' is the wordplay.
'problem' indicates an anagram.
'picnickers'+'ant'='picnickersant'
'picnickersant' with letters rearranged gives 'PANIC-STRICKEN'.
(Other definitions for panic-stricken that I've seen before include "Scared stiff" , "Unnerved" , "Frenzied" , "Terrified" .)