Little creatures are found in such groups (5)
I believe the answer is:
sects
'such groups' is the definition.
'sects' can be an answer for 'groups' (I have seen 'Religious groups ' mean 'sects' so perhaps 'groups' could also mean 'sects'). I'm unsure of the 'such' bit.
'little creatures are found in' is the wordplay.
'little' says to take the initial letters.
'are found' becomes 'sets' (I can't explain this - if you can you should give a lot more credence to this answer).
'in' means one lot of letters goes inside another.
The initial letter of 'creatures' is 'c'.
'c' put inside 'sets' is 'SECTS'.
Can you help me to learn more?
(Other definitions for sects that I've seen before include "Religious factions" , "Groups of people with divergent religious beliefs" , "Dissenting cliques" , "Orders" , "Groups of people with unconventional religious beliefs" .)