Stinging arachnid (8)
I believe the answer is:
scorpion
'stinging arachnid' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for scorpion that I've seen before include "can sting one" , "Stinging creature" , "Sting-tailed creature" , "Venomous creature" , "Kind of spider with pincers and stinging tail" .)