Possibly fly in a group (6)
I believe the answer is:
insect
I believe this is a double definition.
'possibly fly' is the first definition.
(I've seen this before)
'a group' is the second definition.
(I know that insect taxon rank class)
'in' is the link.
(Other definitions for insect that I've seen before include "Small invertebrate creature" , "Eg, beetle or fly" , "Invertebrate, often winged" , "Soldier perhaps" , "Small invertebrate arthropod" .)