Small cationic peptides that are an important component, in most species, of early innate and induced defenses against invading microbes. In animals they are found on mucosal surfaces, within phagocytic granules, and on the surface of the body. They are also found in insects and plants. Among others, this group includes the defensins, protegrins, tachyplesins, and thionins. They displace DIVALENT cations from phosphate groups of membrane lipids leading to disruption of the membrane.