Jackson had been a keen naturalist since his youth and though he later focussed on entomology was also an ornithologist and botanist. In 1935 he participated in the
British Museum expedition to the
Rwenzori Mountains with the dipterist
Frederick Wallace Edwards and the botanist
George Taylor. The expedition contributed large numbers of moths, butterflies and beetles to the museum collection. Shortly after this expedition Jackson began his own collection of butterflies and writing academic papers on his finds. His favourite families were the
Nymphalidae and the
Lycaenidae. In Kenya Jackson amassed one of the world's finest collections of African butterflies, collected in his spare time and on expeditions across Africa. It was the largest collection of native butterflies in Africa. Jackson developed new techniques of capturing and breeding the insects and trained black staff who collected specimens for him in Kenya, Uganda, Tanzania, Middle Congo, Cameroun, Nigeria and the Ivory Coast. At the time of his death he was negotiating with the government of Gabon to send his collectors there. He collected hundreds of new species. He wrote a number of journal articles on many of his discoveries but his publications were relatively little, compared to his collection. He began writing only at the age of 34 and there were long intervals between his early papers. His output increased in the late 1950s. His most important works are perhaps his early 1960s works on the
Epitola and his collaboration with
Victor Van Someren on mimicry in African butterflies. In 1961 Jackson sent around half of his collection, some 65,000 specimens to the British Museum, feeling it would benefit from being more readily available to the scientific community. He often visited the museum to study its collection and compare them to new species he had collected. Through the museum Jackson began a long professional association with French entomologist
Henri Stempffer. As well as the donation to the British Museum Jackson donated thousands of specimens to other collections including those of the
National Museum of Natural History, France, the Belgian
Royal Museum for Central Africa and Stempffer's private collection. On his death the remainder of his entomological collection, around 65,000 specimens, as well as his library, was left to the
Kenyan National Museum at Nairobi. ==Works==