Insect nest (5)
(Other definitions for anthill that I've seen before include "Home for social workers?" , "There's much work to be done here" , "Mountain (of insects)" , "Termite mound" , "Many a worker here" .)
'insect nest' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for nidus that I've seen before include "focus of infection" , "nerve-centre" .)