Rattus exulans is the smallest of the three rats (Rattus rattus, R. norvegicus and R. exulans) closely associated with humans. R. exulans has a slender body, pointed snout, large ears, and relatively small, delicate feet. A ruddy brown back contrasts with a whitish belly. Mature individuals are 4.5 to 6 inches long (11.5 to 15.0 cm) from the tip of the nose to the base of the tail and weigh 1.5 to 3 ounces (40 to 80 g). The tail has prominent fine scaly rings and is about the same length as the head and body. Female R. exulans have 8 nipples, compared to 10 and 12 nipples normally found on R. rattus and R. norvegicus, respectively. Morphology (skull size) of R. exulans has been shown to vary with latitude and island size. This effect is most pronounced in the tropics.