Decent pie ruined by creepy-crawly (9)
I believe the answer is:
centipede
'creepy-crawly' is the definition.
(centipede is a kind of invertebrate)
'decent pie ruined' is the wordplay.
'ruined' is an anagram indicator.
'decent'+'pie'='decentpie'
'decentpie' is an anagram of 'CENTIPEDE'.
'by' acts as a link.
(Other definitions for centipede that I've seen before include "Many-legged animal" , "Myriapod" , "Many-legged insect" , "Creepy type" , "Many-legged creature" .)