[1][2] Kirby devoted most of his career to the study of protists, specifically those flagellates that live in termite digestive tracts.
[3] Harold Kirby was concerned not only with protozoölogy and parasitology; he was also a naturalist who loved field work.
Upon his death he was survived by his widow (who held a higher degree in zoology), a daughter, and a son.
His successor was William Balamuth, who received his Ph.D. in 1939 with Kirby as thesis advisor and in whose honor the amoebic genus Balamuthia is named.
[4][5] William Balamuth and Dorothy Riggs Pitelka (1920–1994) played an important role in maintaining U. C. Berkeley's strong program in protistology started by Kofoid and Kirby.