W. Frederick Purcell was the son of Dr Walter P.J. Purcell of Waterford, Ireland, and his wife Sophia W.J. Herzog of Cape Town. The family settled in Cape Town in 1868. Much of Purcell's childhood was spent at Bergvliet, a farm and historic home owned by his maternal uncle, W.F. Herzog, and originally part of W.A. van der Stel's* farm Groot Constantia. The wildlife on the farm may have stimulated his interest in zoology, while its flora occupied him during his later years.
Purcell studied at the South African College, Cape Town, from 1881. He matriculated through the University of the Cape of Good Hope in 1884, and obtained the Bachelor of Arts (BA) degree with Honours in mathematics and natural science at the same institution in 1887. While still a student he presented coleoptera from Constantia (presumably collected on Bergvliet) to the South African Museum in 1885, followed by more insects collected at Prieska in 1887.
After graduating Purcell continued his zoological studies in Germany, his main interest being the internal structure of arachnids. The Friedrich-Wilhelms-Universität, Berlin, awarded him the degree Doctor of Philosophy (Dr Phil) in 1894 with a thesis entitled Ueber den Bau der Phalangidenaugen (On the structure of the eyes in the Phalangida, 60p), published in the Zeitschrift für wissenschaftliche Zoologie that same year. It was followed the next year by his "Notes on the development of the lungs, entapophyses, tracheae and genital ducts in spiders" in the Zoologischer Anzeiger.
Back in South Africa he donated his collection of South African Coleoptera (Families Cicindelidae and Carabidae), as well as a collection of European Coleoptera and Rhynchota, to the South African Museum in 1895, followed by the rest of his insect collections the next year. Also in 1895 he applied for the post of director of the museum, following the resignation of Roland Trimen*. He did not get the post, probably because of his lack of museum experience. That same year he became a member of the South African Philosophical Society. When the latter became the Royal Society of South Africa in 1908 he was elected one of its first Fellows, and in 1917 served on its council. He joined the British Association for the Advancement of Science in 1905 and the South African Association for the Advancement of Science in 1910. At some time he became a corresponding member of the Zoological Society of London. From 1900 to 1903 he was an examiner in zoology for the University of the Cape of Good Hope.
On 1 July 1896 Purcell was appointed first assistant and keeper of the Land Invertebrate collection (except insects) in the South African Museum, under its new Director, W.L. Sclater*. He stayed on in this post until 1905 and during this time established himself as the founder of southern African arachnology. Most of his work during this period was published in the Annals of the South African Museum (initiated in 1898) and the Transactions of the South African Philosophical Society. He described new South African spiders (Transactions, 1902(2), 1904; Annals, 1903; Annals and Magazine of Natural History, 1907) and initiated the local systematic study of spiders, giving keys as well as full descriptions of the species of many families. He gave considerable attention to the Mygalomorpha (four-lunged spiders), but also made original contributions to other groups. His work on South African scorpions included the description of many new species (Annals, 1898, 1899(2), 1901). He initiated the systematic study of South African scorpions, made an outstanding study collection, and placed the group on a firm taxonomic basis. He provided the first descriptions of local Solifugae ("Jerrymanders", Annals, 1899), including new genera (Annals, 1903), and accumulated a large collection. As the first zoologist in Africa to make a thorough study of Peripatus he extended the earlier taxonomic work of H.N. Moseley*, A. Sedgwick* and others, described a new genus endemic to South Africa, and added three new species to the faunal list (Annals, 1899, 1900). In 1905 he contributed a chapter on South African land and fresh-water invertebrates (excluding molluscs and insects) to the volume Science in South Africa (Flint & Gilchrist, 1905), published in preparation of the joint meeting of the British and South African Associations for the Advancement of Science later that year. At the meeting he read a paper, "On some early stages in the development of Peripatus Balfouri", in which he improved on Sedgwick's description of the ova by using better preserved specimens. He was a keen collector of both terrestrial and marine invertebrates and was commemorated in the names of the non-marine molluscs Euonyma purcelli and Apera purcelli (both since renamed).
Some of the new species of Arachnida he described were collected by himself and his wife Anna; others had been collected by, among others, S.C. Cronwright-Schreiner* (Annals, 1903), Reverend H.A. Junod* (Novitates zoologicae, 1903), and Professor L.S. Schultze* (published in Germany, 1908). The spider genus Purcelliana was named after him by J.A.L. Cooke in 1964, in recognition of his descriptive work on the family Prodidomidae.
In July 1905 Purcell resigned his post owing to ill health and retired to Bergvliet, which by this time belonged to his mother and her sister. Until his death in 1919 at the age of 53 he remained there and managed the farm on behalf of the family. At the same time he continued to collect arachnids and insects, continued some of his work as an honorary keeper at the South African Museum to 1908, and published Development and origin of the respiratory organs of Araneae (London, 1909, 110p). However, his main scientific activity during his retirement was to make a complete herbarium of the farm's well-preserved natural vegetation (the property was later developed into a suburb of Cape Town). His herbarium eventually comprised over 2500 sheets and after his death his widow presented it to the herbarium of the South African Museum. It is now in the Compton Herbarium, National Botanical Institute, Cape Town.
Purcell's historic home, connections to influential Cape families and friendship with Mrs Marie Koopmans-De Wet brought about a life-long interest in Cape history, art and antiques. He was largely responsible for the South African Museum acquiring the Koopmans-De Wet house in 1911 and its conversion into a museum of South African antiquities, and became its honorary curator. The house was opened to the public in March 1914 and was later proclaimed a historical monument.