Crawler popular with cult (6)
I believe the answer is:
insect
'crawler' is the definition.
(I know that insect is a type of crawler)
'popular with cult' is the wordplay.
'popular' becomes 'in' ('in' can mean trendy).
'with' means one lot of letters go next to another.
'cult' becomes 'sect' (religious sect).
'in'+'sect'='INSECT'
(Other definitions for insect that I've seen before include "Contemptible person" , "Worthless person" , "Fly, say?" , "Segmented invertebrate" , "Six-legged animal" .)