Throughout her life, Comstock illustrated her husband's lectures and publications on insects. She had no formal training in this illustration; she would study an insect under a microscope then draw it. While her husband was chief entomologist in the U.S. Department of Agriculture from 1879 to 1881, she prepared the drawings for his 1880 "Report of the Entomologist" on citrus scale insects. She then reentered Cornell and received a degree in natural history in 1885. She studied wood engraving at Cooper Union, New York City, so she could prepare illustrations for her husband's book "Introduction to Entomology" in 1888. Also in 1888, she was one of the first four women admitted to Sigma Xi, a national honor society for the sciences.