Johann Kaspar Füssli, also written Johann Caspar Fuesslins or Fuessly (9 March 1743 – 4 May 1786), was a Swiss painter, entomologist and publisher.
He was born in Zurich, the son of Johann Caspar Füssli (3 January 1706 – 6 May 1782) and Anna Elisabeth Waser. He was thus the brother of Henry Fuseli (Johann Heinrich Füssli) (3 December 1745 – 17 April 1825).
The only spider species he described (as Fuesslin, 1775) is the daddy long-legs spider, Pholcus phalangioides, also known as cellar spider.
He died, aged 43, in Winterthur.