Insect shell-like on rug (6)
I believe the answer is:
earwig
'insect' is the definition.
(earwig is a kind of insect)
'shell-like on rug' is the wordplay.
'shell-like' becomes 'ear' (I've seen this before).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'rug' becomes 'wig' ('rug' is an informal term for a wig).
'ear'+'wig'='EARWIG'
(Other definitions for earwig that I've seen before include "flatterer" , "Pincered insect" , "Small insect with aural toupee?" , "Common garden insect" , "creepy-crawly" .)