Ferdinand Anton Franz Karsch (2 September 1853, in Münster – 20 December 1936, in Berlin) was a German arachnologist, entomologist and anthropologist.

He also wrote on human and animal sexual diversity with his mother's maiden name included as Ferdinand Karsch-Haack from around 1905.

The son of doctor Anton Karsch, he was educated at the Friedrich Wilhelm University in Berlin and published a thesis on the gall wasp in 1877.

Alongside his zoological activities, he published many works on sexuality and, in particular, homosexuality in both the animal kingdom and in so-called "primitive" peoples, including Das gleichgeschlechtliche Leben der Kulturvölker – Ostasiaten: Chinesen, Japanese, Korea in 1906 on homosexuality in East Asian societies and in 1911 Das gleichgeschlechtliche Leben der Naturvölker on homosexuality in Africa and indigenous societies of Asia, Australia and the Americas.

The rise of Hitler to power and Nazi repression of homosexuality led to the eclipse of his reputation.