Insects do not have an organ equivalent to the human liver, a center of energy storage (glycogen) and metabolism. These functions in insects are predominantly performed by a disorganized tissue called “fat body”. In 1665, Robert Hooke turned his microscope to study insects and insect structures which he published in “Micrographia”*. In his study of the human louse (an easily collected insect at the time) Hooke described a large body in the abdomen which he call the liver. It was not until the 1900s that insect biologists concluded that the structure was not at all a liver but a mycetome, a structure that houses symbiotic microorganisms. The mycetome provides the symbionts with a stable sheltered home and access to excess nutrients consumed by the lice. The symbionts are capable of synthesizing essential nutrients that the lice themselves cannot make and do not obtain in their blood feeding. Killing the symbionts with antibiotic treatments has a negative effect on the lice.
*Hooke, R. 1665. Micrographia: or Some Physiological Descriptions of Minute Bodies Made by Magnifying Glasses with Observations and Inquiries Thereupon. Council of the Royal Society of London for Improving Natural Knowledge, London.