Charles Eustace Pillans (better known as Eustace Pillans), civil servant in the Cape Colony, was the second son of the commercial pioneer Charles Stuart Pillans (1785-1849) and his wife Alida D. Colyn, and an older brother of Charles Roland Pillans*. Eustace was married to Mary E.S. Porter, with whom he had only one son, the botanist Neville S. Pillans*. After completing his schooling at the Diocesan College, Rondebosch (Cape Town), Eustace travelled all over southern Africa, visiting, among others, Namaqualand, Natal, the Orange Free State, and the Transvaal. He started his career in the civil service of the Cape Colony in November 1873, as third clerk in the Audit Office, and was transferred to the General Post Office in August 1876. During the Ninth Frontier War of 1877-1878 he served with the rank of lieutenant as acting adjundant in Carrington's Frontier Light Horse and was awarded a medal. A few years later, during the Basuto War of the Guns (1880-1881), he served with the rank of lieutenant in the Duke of Edinburgh's Own Volunteer Rifles. In March 1884 he was appointed inspector and surveyor of post offices in the Cape Colony and in this capacity travelled all over the colony.
Pillans had various scientific interests. For example, at a meeting of the South African Philosophical Society on 25 October 1882 a letter from him was read in which he described his observations of an exploding meteor (he was not a member of the society); in July 1885 he became the first honorary treasurer of the City and Suburban Horticultural Society; as honorary secretary of the Cape Fruit-Growers' Association he published the association's "Bye laws" in the Agricultural Journal of the Cape of Good Hope in June 1893; he served on the committee of the Western Province Agricultural Society; and in 1908 he presented a coal sample from Bamboo Siding (north-west of Molteno) to the South African Museum. His interest in agriculture and horticulture led to a major career change in March 1893, when he was appointed agricultural assistant in the Cape Department of Agriculture, a post he held to the end of January 1902. The letter book he kept at the Constantia wine farm from 1896 to 1899 is in the National Library of South Africa in Cape Town. During these years he presented plants to P. MacOwan*, Curator of the Cape Government Herbarium (1896, 1897). As co-author with MacOwan he took part in writing a Manual of practical orchard work at the Cape, a monograph that was published as Pamphlet No. 4 (1896, 110p) of the Department of Agriculture.
In 1901 Pillans became manager of the Agricultural Settlement Bureau created by the British authorities in the Orange River Colony (now the Free State) after the occupation of that territory during the Anglo-Boer War (1899-1902). However, he soon returned to the Cape Colony, where he held various positions in the civil service from February 1902 to 1905, among them director of the government labour bureau plus immigration officer from July 1902 to 1904. From 1905 to 1910 he was horticultural assistant in the Cape Department of Agriculture. In recognition of his work he was awarded the Imperial Service Order (ISO) in 1907, a decoration confined to members of the British civil service. He remained in the Department of Agriculture after the formation of the Union of South Africa in 1910 and wrote three short articles for the Agricultural Journal (Union of South Africa) in 1911: "The date palm", "Notes on the cultivation of the olive tree at the Cape", and "Notes on the loquat". He collected and cultivated succulent plants in his garden in Rosebank and sent specimens, including several new species, to N.E. Brown* at Kew Gardens. Euphorbia eustacei was named after him by Brown, and Erica eustacei by Mrs H.M.L. Bolus*. His collection of plants was later taken over by his son.