Remembered best for his work in the parasitology sub-field of malariology (the study of malaria), this Italian zoologist and doctor also studied the behavior, development, and life cycles of termites, eels, and honey bees. He was the 1896 recipient of the Darwin Medal.
After earning a medical degree from the University of Pavia, he worked at the Zoological and Oceanographic Stations in Naples, Italy, and went on to study at Germany's University of Heidelberg.
He taught zoology at the University of Catania and anatomy at the Sapienza University of Rome.
He was born in Rovellasca, Italy, to Costanza Mazzuchelli and Luigi Grassi.
Were it not for the influence of microbiologist Robert Koch, who favored doctor and malaria researcher Ronald Ross for the prize, Grassi would have been at least a dual recipient of the 1902 Nobel Prize in Physiology or Medicine.