Felt these bats surrounding adult -- they come out at night (5,5)
I believe the answer is:
false teeth
'they come out at night' is the definition.
(false teeth are removed over night)
'felt these bats surrounding adult' is the wordplay.
'bats' is an anagram indicator (slang for mad).
'surrounding' means one lot of letters goes inside another.
'adult' becomes 'a' (abbreviation).
'felt'+'these'='feltthese'
'feltthese' is an anagram of 'flseteeth'.
'flseteeth' placed around 'a' is 'FALSE TEETH'.
(Other definitions for false teeth that I've seen before include "Denture's components" , "New gnashers!" , "Choppers that may be taken out" , "Plates" , "set out at night" .)