Small disgusting tailless insect (6)
I believe the answer is:
weevil
'insect' is the definition.
(weevil is a kind of insect)
'small disgusting tailless' is the wordplay.
'small' becomes 'wee' ('wee' can be similar in meaning to 'small').
'disgusting' becomes 'vile' (I've seen this before).
'tailless' means to remove the last letter.
'vile' with its last letter taken away is 'vil'.
'wee'+'vil'='WEEVIL'
(Other definitions for weevil that I've seen before include "Kind of beetle that damages crops" , "Type of beetle that feeds of stored grain etc" , "Insect that feeds on plant products" , "little creature" , "Small beetle that feeds on plants" .)