Frank Cruden passed the intermediate examination of the University of the Cape of Good Hope (equivalent to the first year of study for the BA degree) in 1903. From 1911 or earlier to at least 1918 he resided in Alicedale, Eastern Cape, but during the nineteen-twenties he was a master at the Grey High School in Port Elizabeth. He was interested in several branches of natural history, particularly in spiders. Many of the specimens he collected were presented to the Albany Museum, Grahamstown. In 1910 he donated four stone artefacts found at Stellenbosch, including an unusually large digging stone. During the next few years he supplied the museum with zoological material, including many centipedes and some Peripatus (1912), reptiles and arachnids (1913), and ants (1914). He also presented plant specimens to the museum in 1912 and during the nineteen-twenties.
Cruden's studies of spiders and other invertebrates formed the basis of three papers. His "Notes on the habits of a few trap-door spiders found in Alicedale, Cape Province" was published in the Report of the South African Association for the Advancement of Science in 1915 (pp. 601-611), followed by "Note on the occurrence of trapdoor caterpillars at Alicedale" (Ibid, 1916, pp. 196-197). Years later he published a note "On the spider Argiope australis" in the South African Journal of Natural History (1926, Vol. 6(1), pp. 49-51). He became a member of the South African Association for the Advancement of Science in 1916.