Hippo, perhaps, with its head beset by insects (8)
I believe the answer is:
behemoth
'hippo perhaps' is the definition.
(behemoth can mean a large animal)
I don't understand the remainder of the clue.
(Other definitions for behemoth that I've seen before include "Something huge and monstrous" , "Giant" , "Great beast of the Bible" , "Monstrous beast, or thing" , "Big corporation" .)