Arnold Wilhelm Spilhaus, businessman, served a four year apprenticeship with a wholesale firm in Lübeck before being employed by Messrs Lippert Brothers, a well-known German-South African trading concern in Hamburg. He came to South Africa for the firm in 1869 and spent two years investigating the possibilities of trading along the Natal and Mozambique coasts. As part of this venture he also explored the Zambezi River. In September 1871 he opened a branch of Lippert Brothers in Cape Town and managed it until December 1876. Early in 1873 he married Lydia M. Sedgwick, with whom he had three sons and four daughters.
Spilhaus collected plants, mainly during the eighteen-seventies, most of which went to the Lübeck Museum. They are usually quoted as having been collected by "Spielhaus". The museum's herbarium went to the Botanical Museum at Berlin-Dahlem in 1915. Among others he made a collection of algae in the vicinity of Cape Town which was sent to Professor Schmitz of Greifswald, Germany. The collection was inspected by Barton (1893) but appeared to contain no new species.
In December 1876 he and Herbert Wilman of Beaufort West founded the firm Wilman, Spilhaus & Co. Originally it traded mainly in wool, hides and imported products, but later acquired other interests, including diamonds and agricultural machinery. Spilhaus's work for the firm regularly took him on journeys inland to buy produce. After Wilman retired towards the end of 1895 he continued the business as Wm Spilhaus & Co. Having decided to remain in South Africa he became a British subject in 1891. In July 1915 the firm was made a limited liability company of which he became governing director, while two of his sons and a son-in-law were directors.
Spilhaus had wide cultural interests and was an early patron of South African art. He spoke several European languages fluently and towards the end of his life published some entertaining pamphlets dealing with his philosophical speculations. He remained a prominent citizen of Cape Town until his death at the age of 100. His Reminiscences and family records, edited by M. Whiting Spilhaus, were published a few years after his death (Cape Town, 1950).