He inherited his father's love of natural science, and like him spent much time, energy, and money in carrying out investigations which were of great use to Queensland.
By breeding the common house mosquito (Culex fatigans) and allowing the insects to bite a person suffering from filaria he showed that the parasite lived and developed in them.
His numerous other researches included the testing of snakebite cures, the investigation of mange on horses, and an inquiry into the economics of the distillation of eucalyptus oil from native eucalypts.
After noting the diminishing numbers of these "living fossils," he advocated their protection and proposed the establishment of a breeding station at Stradbroke Island.
He looked forward to being able to end his days, as he thought, in comfort, with a reasonable amount of leisure and some facilities for experimenting with cotton and lungfish.
Although the heat and humidity made him sick, and there was no water suitable for irrigation, he attempted to grow his cotton varieties, cuttings of which he had brought from Eidsvold.
He firmly believed that it was his duty to improve the living conditions of the Aboriginal people, and was not afraid publicly to criticise the location and management of the settlement.
[2] In May 1932, he left Palm Island for Wallaville near Bundaberg to semi-retire, looking forward to the freedom and leisure of a small medical private practice and furthering his research work.
Shortly before his death in 1933, he was described as follows:[2]"Bancroft is a living example of the old saying that a prophet is without honour in his own country, this often applies also to scientists, and to any man who is rather different from and greatly superior to his fellows.
Their daughter Mabel Josephine (Jo) Bancroft (1896–1971) became a noted parasitologist, researching cattle ticks, sheep blowfly and malaria.