For Linnaeus, say, maggot active isn't bad (8)
I believe the answer is:
botanist
'for linnaeus say' is the definition.
(linnaeus is a kind of botanist)
'maggot active isn't bad' is the wordplay.
'maggot' becomes 'bot' (bot is a type of maggot).
'active' becomes 'a' (grammatical abbreviation).
'bad' indicates an anagram.
'isnt' with letters rearranged gives 'nist'.
'bot'+'a'+'nist'='BOTANIST'
(Other definitions for botanist that I've seen before include "Someone studying plants" , "Expert in plant biology" , "Plant studier" , "Scientist who studies plants" , "Banks" .)