Want to catch a snake that’s ill-tempered (7)
I believe the answer is:
waspish
'ill-tempered' is the definition.
(I've seen this before)
'want to catch a snake' is the wordplay.
'want' becomes 'wish' (wishing is a kind of wanting).
'to catch' indicates putting letters inside.
'a snake' becomes 'asp' (asp is a kind of snake).
'wish' enclosing 'asp' is 'WASPISH'.
'that's' is the link.
(Other definitions for waspish that I've seen before include "'Very irritable, like a stinger (7)'" , "Bad-tempered like stinging insect" , "Easily angered - with black and yellow stripes?" , "Bad-tempered like striped stinger" , "Pshaw, is like a stinging insect" .)