She was the daughter of Bob Ormerod, F.R.S., author of The History of Cheshire, and was born at Sedbury Park, Gloucestershire. From her earliest childhood insects were her delight, and the opportunity afforded for entomological study by the large estate upon which she grew up and the interest she took in agriculture generally soon made her a local authority upon this subject. When, in 1868, the Royal Horticultural Society began forming a collection of insect pests of the farm for practical purposes, Miss Ormerod largely contributed to it, and was awarded the Flora medal of the society.
In 1877 she issued a pamphlet, Notes for Observations on Injurious Insects, which was distributed among persons interested in this line of inquiry, who readily sent in the results of their researches, and was thus the beginning of the well-known Annual Series of Reports on Injurious Insects and Farm Pests. In 1881 Miss Ormerod published a special report upon the turnip-fly, and in 1882 was appointed consulting entomologist to the Royal Agricultural Society, a post she held until 1892. For several years she was lecturer on scientific entomology at the Royal Agricultural College, Cirencester.
Her fame was not confined to England: she received silver and gold medals from the university of Moscow for her models of insects injurious to plants, and her treatise on The Injurious Insects of South Africa showed how wide was her range. In 1899 she received the large silver medal from the Socite Nationale d'Acclimatation de France.
Her work on natural history was widely cited and she undertook brave experiments:
Among others of her works are the Cobden Journals, Manual of Injurious Insects, and Handbook of Insects injurious to Orchard and Bush Fruits. Almost the last honour which fell to her was the honorary degree of LL.D. of Edinburgh University - a unique distinction, for she was the first woman upon whom the university had conferred this degree. The dean of the legal faculty in making the presentation aptly summoned up Miss Ormerod's services as follows:
She died at St Albans.