Stelfox, Arthur Wilson (1883–1972), naturalist and entomologist, was born 15 December 1883 in Belfast, youngest child among at least two sons and two daughters of James Stelfox, MICE, and his wife Jennie or Jane (née McIlwaine). His father was associated with Belfast Gas Works, and his mother was the thirteenth of fourteen children of William McIlwaine (1807–85), rector of St George's, Belfast, who was noted for liturgical innovation, for his anti-catholic views, and for open-air preaching. Stelfox was educated at Campbell College, Belfast, trained as an architect, worked in London, and became ARIBA (1909). He belonged to the North of Ireland Cricket and Rugby Club and played in interprovincial matches in both sports. His father had been a member of Belfast Naturalists’ Field Club since 1882, and members frequently met in the Stelfox home. Stelfox took part in club excursions in his youth, and became a club member in 1903.
His first published paper was ‘The molluscs of Bushy Park, Dublin’ in the Irish Naturalist (1904). He became joint secretary of the Belfast Naturalists’ Field Club in 1908. Already an acknowledged conchologist, Stelfox was invited to join the Clare Island survey, and in July 1911 he spent, with Robert Lloyd Praeger (qv) and others, several days working on the natural history of the adjacent islands. His comprehensive report was published in 1912, in which year he was elected MRIA. He married (1914) Margarita Dawson Mitchell, another amateur naturalist and Field Club member. Two of their children died young, and a son survived. During the first world war, the Stelfoxes lived and worked in Ballymagee, Co. Down, as fruit-growers. In 1920 Arthur Stelfox became an assistant naturalist in the National Museum in Dublin where he remained until retirement in 1948, specialising in study of land and freshwater mollusca, hymenoptera (insects with membranous wings such as bees, wasps, and saw-flies), and prehistoric animal remains in caves. In 1924 he was placed in sole charge of the National Museum's zoological collection. He greatly influenced younger men such as G. F. (‘Frank’) Mitchell (qv).
An authority on hymenoptera, he also studied odonata (grasshoppers and dragonflies), lepidoptera (butterflies), and coleoptera (beetles). The following year he played a key role in establishing the Irish Naturalist's Journal. He published many papers in the Journal on the mollusca of Donegal and Galway, on caves in Carrigtwohill, Co. Cork, and on the flora of the Galtee Mountains and the Glen of Aherlow, Co. Tipperary. Irish entomology (1984) lists ninety-nine papers by Stelfox on hymenoptera in such journals as RIA Proc., the Entomologist's Monthly, and the Irish Naturalist's Journal. His ‘List of hymenoptera aculeata’ in RIA Proc. (1924) raised the known number of the species in Ireland from 122 to 175, and in later work he further added to the number. No other Irish entomologist made such significant contributions to the study of hymenoptera.
Although he twice refused offers of honorary degrees, he was proud of his election in 1947 as honorary fellow (or associate) of the Linnaean Society. After his retirement in 1948 he continued contributing papers, reviews, and obituaries to various journals; he was particularly interested in parasitic hymenoptera. No one knew as much about Irish fauna in general as did Stelfox. The garage of his home at Clareville Road, Harold's Cross, Dublin, was lined with boxes of lepidoptera and sawfly larva, and he grew examples of rare native flora in his garden. In 1956 he returned to Northern Ireland, to a newly built house at Newcastle, Co Down. In October 1966 Stelfox donated his meticulously labelled collection of 90,000 Irish hymenoptera to the Smithsonian Institution, Washington, DC. He chose the Smithsonian because he wanted to see the collection housed somewhere that did not already possess an extensive inventory. His was the largest ever collection of Irish hymenoptera; Stelfox had been collecting in all thirty-two Irish counties for over fifty years. A team of six senior entomologists in the US department of agriculture and at the Smithsonian found the collection invaluable in their research, and specimens were made available to other American museums. Parts of the Stelfox collection were loaned to museums in Budapest, Munich and Vienna. The native plant collection at the National Botanic Gardens, Glasnevin, Dublin, held important contributions derived from Stelfox's garden. His wife, Margarita Dawson Mitchell Stelfox (d. 1971), studied mycetozoa (slime moulds), and published regularly in the Irish Naturalist. Arthur Stelfox died 19 May 1972 and was buried at Newcastle, Co Down. His grandson Dawson Stelfox became an architect and noted mountaineer, the first Irishman to reach the summit of Mount Everest (May 1993).