Character in Lewis Carroll book Alice's Adventures in Wonderland depicted at the Hatter’s mad tea-party with straw on his head (5,4)
I believe the answer is:
march hare
(Other definitions for march hare that I've seen before include "character encountered by Alice" , "seen at endless party" , "Proverbially mad creature" , "Character at the tea-party in Alice's Adventures in Wonderland" , "Ditto" .)