Mass of bees (5)
I believe the answer is:
swarm
'mass of bees' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for swarm that I've seen before include "Moving crowd, of bees say" , "Flight of bees" , "Horde" , "Body of bees" , "Go to form new colony" .)