Needing to trap fox, secret lodger lost elephant (8)
I believe the answer is:
mastodon
'lost elephant' is the definition.
(mastodons were elephant-like creatures)
'needing to trap fox secret lodger' is the wordplay.
'needing to trap' is an insertion indicator.
'fox' becomes 'tod' (historic term).
'secret lodger' becomes 'mason' (Freemasons meet in lodges).
'tod' inserted inside 'mason' is 'MASTODON'.
(Other definitions for mastodon that I've seen before include "old jumbo" , "dead hairy beast" , "Extinct beast" , "Big beast" , "Prehistoric creature" .)