As a boy, Thomas Say, born into a prominent Quaker family in Philadelphia, often visited the family garden, Bartram’s Garden, where he could take butterfly and beetle specimens to his great-uncle William.
A self-taught naturalist, he became an apothecary, and helped found the Academy of Natural Sciences of Philadelphia in 1812.
He served as librarian for the Academy of Natural Sciences of Philadelphia, curator at the American Philosophical Society, and professor of natural history at the University of Pennsylvania
In 1816, he met Charles Alexandre Lesueur, a French naturalist, malacologist, and ichthyologist who soon became a member of the Academy and served as its curator until 1824.
To collect insects, Say made expeditions to the frontier, in spite of the risk of attacks by American Indians and the hazards of traveling in wild countryside.
In 1818, Say accompanied his friend William Maclure, then the ANSP president and father of American geology; Gerhard Troost, a geologist; and other members of the Academy on a geological expedition to the off-shore islands of Georgia and Florida, then a Spanish colony.
In 1819–20, Major Stephen Harriman Long led an exploration to the Rocky Mountains and the tributaries of the Missouri River, with Say as zoologist.
Their official account of this expedition included the first descriptions of the coyote, swift fox, western kingbird, band-tailed pigeon, rock wren, Say’s phoebe, lesser goldfinch, lark sparrow, lazuli bunting, and orange-crowned warbler.
In 1823, Say served as chief zoologist in Long’s expedition to the headwaters of the Mississippi River.
He traveled on the “Boatload of Knowledge” to the New Harmony Settlement in Indiana (1826–34), a utopian society experiment founded by Robert Owen.
He was accompanied by Maclure, Lesueur, Troost, and Francis Neef, an innovative education reformer.
There he later met Constantine Samuel Rafinesque-Schmaltz, another naturalist.
Say married Lucy Way Sistare, whom he had met as one of the passengers to New Harmony, near the settlement.
She was an artist and illustrator of specimens, as in the book American Conchology, and was elected as the first woman member of the Academy of Natural Sciences
Say was a modest and unassuming man, who lived frugally, like a hermit, in New Harmony. He abandoned commercial activities and devoted himself to his studies.
He died, apparently from typhoid fever, when he was 47 years old.
The quality of the plates, in his book on American insects, and the clarity of Say’s description won him immediate fame abroad, and he was made a foreign member of the Linnean Society of London.
Say named some 1,500 new species – many of his discoveries (such as the American dog tick) were crucial for the future study and control of disease in humans, livestock and crops