Spotted her, say, black widow, say (6)
I believe the answer is:
spider
'black widow say' is the definition.
(I know that Latrodectus mactans is a type of spider)
'spotted her' is the wordplay.
I cannot really understand how this works, but
'her' could be 'de' and 'de' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
'say' acts as a link.
Can you help me to learn more?
(Other definitions for spider that I've seen before include "Bruce's inspiration?" , "Member of arachnid family" , "Snooker equipment" , "Webster" , "Small creature" .)