[1][2] In 1892, Aldrich traveled to the University of Kansas where he was befriended by Samuel W. Williston who lent him money and encouraged him to stay at his house.

He began to assemble his most important work, Catalogue of the North American Diptera, published by the Smithsonian in 1905.

In 1893, he married Ellen J. Roe from Brookings, South Dakota, but after only four years of marriage, his wife and their infant son died.

[1][2] In 1906, Alderich took a sabbatical to attend Stanford University where he submitted his Catalogue as a doctoral thesis and was awarded a Ph.D. in 1907.

"[2] Aldrich had a national reputation as a talented entomologist and he was quickly hired into the USDA Bureau of Entomology and stationed in Lafayette, Indiana.

[4] After the death of Frederick Knab in 1918, Aldrich became the Associate Curator of Insects and the Custodian of Diptera at the United States National Museum in Washington, D.C., a position he held until his death[1][4] Throughout his career, Aldrich was a prolific collector of insects and was known for his ability to find rare species.

He also donated to the museum a card catalog file of North American literature on these specimens.

[2][5] Aldrich was active in the All Souls Unitarian-Universalist Church in Washington, D.C., where he taught religion classes.