Bats are able to develop (9)
I believe the answer is:
elaborate
'develop' is the definition.
(elaborating is a kind of developing)
'bats are able to' is the wordplay.
'bats' indicates anagramming the letters (slang for mad).
'are'+'able'+'to'='areableto'
'areableto' is an anagram of 'ELABORATE'.
(Other definitions for elaborate that I've seen before include "Highly detailed" , "Polish" , "flesh out?" , "with added detail" , "Detailed, complicated" .)