Mary Lua Adelia Davis Treat (7 September 1830 in Trumansburg, New York – 11 April 1923 in Pembroke, New York) was a naturalist and correspondent with Charles Darwin. Treat's contributions to both botany and entomology were extensive—four species of plants and animals were named after her, including an amaryllis, Zephyranthes treatiae (now called Zephyranthes atamasca var. treatiae), and an ant species (Aphaenogaster treatiae).
Davis married Dr Joseph Burrell Treat in 1863 and in 1869 they moved to Vineland, New Jersey. Following separation from her husband in 1874, Mary supported herself by publishing popular science articles for periodicals such as Harpers and Queen .
Treat’s first scientific article was a note published in The American Entomologist when she was 39 years old. Over 28 years she wrote 76 scientific and popular articles as well as five books. Her book, Injurious Insects of the Farm and Field, originally published in 1882, was reprinted five times. She also collected plants and insects for other researchers, one of whom was the eminent Harvard botanist Asa Gray. It was through Gray that she was introduced to Charles Darwin. Treat wrote letters to engage in botanical and entomological discourse not only with Darwin and Gray, but Auguste Forel and Gustav Mayr too.
The first recorded correspondence between Treat and Darwin originates from 20 December 1871  in which Treat describes the fly-catching activities of Drosera. Treat and Darwin’s recorded correspondence extends over five years and revolves, unsurprisingly, around the period of time when Darwin was researching, and then publishing, on carnivorous plants. Investigations on these plants are the predominant theme in their correspondence (although not the only theme, they also discussed controlling sex in butterflies), and Treat does not withdraw from openly critiquing Darwin’s hypotheses. One notable exchange concerns the bladderwort plant, Utricularia clandestina.
Darwin’s teacher and mentor at Cambridge, John Stevens Henslow, had a clear understanding of the morphology of Utricularia plants (Walters, 2001), but was perplexed by the working mechanics of their traps. Darwin fared no better with this botanical conundrum, wrongly concluding that animals entered the traps by forcing their heads through the slit-like orifice; their heads serving as a wedge. In a letter to Treat he informs her that this subject drove him ‘half-mad’ (Darwin correspondence 1876). Treat became ‘so deeply interested’ in this plant that ‘she scarcely took note of time’ and describes how ‘the small hours of the morning frequently found her absorbed in her work’ (Treat, 1875). Through long hours of observing the trapping sequence under her microscope she realised that the hairs around the entrance to the trap were sensitive and part of the process by which Utricularia traps opened, contributing new knowledge on the range of microscopic animal prey caught in these traps and the digestive processes they were subjected to. Treat concluded that ‘these little bladders are in truth like so many stomachs, digesting and assimilating animal food’ (Treat, 1875). Darwin was so impressed with Treat’s work on carnivorous plants that he referenced her, both within the main text and in footnotes, throughout his publication Insectivorous Plants (1875). One such reference states that:
‘Mrs Treat of New Jersey has been more successful than any other observer, and has often witnessed in the case of Utricularia clandestina the whole process’ (Darwin, 1875, page 408).
By making such public affirmations of Treat’s scientific work Darwin, as Gianquitto states, ‘takes Treat out of the home, privileges her skill as a professional person, and places her in a dialogue with a circle of established scientists’ (Gianquitto, 2003 p. 149-150). Gianquitto’s opinion is, however, not reflected by all writers discussing Treat’s scientific identity, Norwood, for example, considers Treat to be ‘much more Susan Cooper’s soul-mate than she was Darwin’s colleague’ (Norwood, 1993, p. 42). Rossiter echoes Norwood’s opinion of Treat as inhabiting predominantly domestic spaces, but notes that Treat’s work needs ‘further analysis’ (Rossiter, quoted in Gianquitto, 2003).
In the case of Treat’s correspondence with Darwin a recent increase in the availability of on-line databases has allowed for new research opportunities on their exchanges (see http://www.darwinproject.ac.uk/) and relevant others. Previously Treat’s relationship to Darwin, was filled with what Canning terms, ‘blank spaces, small snapshots and silences’ (Canning, 2005 p. 61). Perhaps Rossiter’s call for ‘further analysis’ can now be answered and further evidence of Treat as ‘Darwin’s colleague’ forthcoming.
The best archive of Treat's life is available at the Vineland Historical Society. The Harvard herbarium has a selection of Treat's specimens sent to Asa Gray and examples of their original correspondence. The Darwin Correspondence Project  has summaries of her correspondence with Darwin, but as yet no full coverage of the contents of their letters to each other. The original letters are, in the main, available to view at Cambridge University Library. The most recently published discussion of Treat's work is in Gianquitto's 'Good Observers of Nature' (2007), however an extensive biography is yet to be written. Despite Darwin writing more letters to Treat than any other female scientific correspondent she is often invisible in contemporary discussions of his life and work.
‘On December 25th I placed tiny bits of raw fresh beef on ten leaves of P. pumila. In six hours the secretion was so copious that the spoon-tipped ends of seven leaves were filled. The secretion had mingled with the juice of the beef and looked bloody, but the meat itself was white and tender. In a little less than twelve hours the fluid had changed colour; it now looked clear, and remained so until it was gradually absorbed ’ (Treat, 1885, p. 169).
- Canning, K. (2006) Gender History in Practice: Historical Perspectives on Bodies, Class and Citizenship. Ithaca and London: Cornell University Press
- Darwin, C. (1875) Insectivorous Plants London: John Murray
- Gianquitto, T. (2003) Nobel Designs of Nature and Nation: God, science and sentiment in women’s representations of American landscape unpublished doctoral thesis Columbia University USA
- Gianquitto, T. (2007) Good Observers of Nature: American Women and the Scientific Study of the Natural World Athens and London: The University of Georgia Press
- Norwood, V (1993). American Women and Nature: Made from this Earth. Chapel Hill and London: North Carolina University Press
- Rossiter, M.W. (1982) Women Scientists in America: Struggles and Strategies to 1940. Baltimore: Johns Hopkins University Press
- Treat, M. (1873) ‘Controlling Sex in Butterflies’. The American Naturalist, 7, 3 pp. 129–132
- Treat, M. (1875) ‘Plants that eat animals’ Gardener’s Chronicle, March, 6th pp. 303–304
- Treat, M. (1882) Injurious Insects of the Farm and Field. New York: Orange Judd Company
- Treat, M. (1885) Home studies in Nature. New York: American Book Company
- Walters, M. (2001) Darwin’s Mentor: John Stevens Henslow 1796-1861 Cambridge and New York: Cambridge University Press