The known physiological functions of serpins in arthropod physiology. The majority of insect serpins are produced in fat body and hemocytes and are then secreted into the hemocoel. In addition, serpins are expressed in a number of additional tissues, including tick and mosquito salivary glands (orange), midgut (green), trachea (blue), and in male accessory glands (MAGs), as well as the venom glands of parasitoid wasps (pink). Major known functions are listed and discussed in detail in the different sections of the manuscript.