Beetle or spaniel eating husks, mostly (10)
I believe the answer is:
cockchafer
'beetle' is the definition.
(cockchafer is a kind of beetle)
'spaniel eating husks mostly' is the wordplay.
'spaniel' becomes 'cocker spaniel' (cocker spaniel is a kind of spaniel).
'eating' means one lot of letters goes inside another.
'husks' becomes 'chaff' (husks of corn).
'mostly' means to remove the last letter (most but not all of the word).
'chaff' with its final letter taken off is 'chaf'.
'cocker' going around 'chaf' is 'COCKCHAFER'.
'or' is the link.
(Other definitions for cockchafer that I've seen before include "plant pest" , "Large beetle destructive of vegetation - frock cache (anag)" .)