Alexander ("Sandy" to his friends and family) was born in 1906 in Washington, D.C. Like most entomologists, Fairchild began his lifelong love affair with insects by collecting butterflies in the fields and barns where he lived.
After a number of magical years travelling with his plant collector father to the jungles of Sri Lanka, Sumatra, and Indonesia, Sandy reluctantly finished high school at age 20, to then attend Harvard, graduating in 1931, in the depths of the Great Depression.
Encouraged by his faculty advisor, Professor Joseph Bequaert, Fairchild chose the Tabanidae, a family of insects known as "horse flies".
He eventually became Assistant, then Acting Director of that research facility in Tropical medicine, funded both by Congress and the Republic of Panamá.
After retiring, Sandy and his wife Elva (whom he married in 1938)[3] moved to Gainesville, Florida, where for the next 25 years, he continued to publish papers and advise graduate students and fellow scientists around the world.