Hearing blood-sucking arachnid, it might be nervous (3)
I believe the answer is:
tic
'it might be nervous' is the definition.
(I know that tic are often nervous)
'hearing blood-sucking arachnid' is the wordplay.
'hearing' shows a homophone (sound like).
'blood-sucking arachnid' becomes 'tick' (I've seen this before).
'tick' sounds like 'TIC'.
(Other definitions for tic that I've seen before include "Minor muscle spasm" , "Twitch in analytical way" , "Convulsive twitch (of face)" , "Facial movement" , "jerk" .)