De Vylder was born in Sweden in 1827. His father, who was from Belgium, married a Swede while being employed by a Swedish family to improve their French. At the age of twelve, he lost his father and was forced to leave school for financial reasons. He learned several languages from his mother and as a talented boy was employed as a tutor in a wealthy family home. He eventually qualified as a land-surveyor and was occupied for a time with mapping and surveying but found that it left him little time to study the natural sciences, especially entomology which had been his main interest from a young age.
From 1844 to 1871 he worked for publishers in Stockholm, illustrating and engraving scientific works. A man of many talents, he trained as a photographer; wrote songs, at least one of which became popular; published poetry, a novel, illustrated children’s books and several plays. With financial help from the Swedish government, he undertook two journeys to the Cape and German South-West Africa (now Namibia). The first was from 1871 to 1875 and again from 1879 to 1887 to collect natural history specimens for Swedish museums.
He was particularly keen to visit Lake Ngami during his second visit to the Cape, but a lack of funds prevented him from journeying northwards, and he remained at the Cape for eight years. He made substantial collections of insects and also wrote poetry and light literary works during this time.
De Vylder was a kind and helpful man who had many friends, though in his diaries he quite frequently criticized others and was particularly scornful of the English. He bore a grudge against the Swedish scientific fraternity for their lack of support, which probably resulted from his lack of formal scientific education. He was, however, an informed, observant, and meticulous collector.