The rhesus macaque is one of the best-known species of Old World monkeys. It is listed as Least Concern in the IUCN Red List of Threatened Species in view of its wide distribution, presumed large population, its tolerance of a broad range of habitats. Native to South and Southeast Asia, rhesus macaque have the widest geographic ranges of any nonhuman primate, occupying a great diversity of altitudes and a great variety of habitats, from grasslands to arid and forested areas, but close to human settlements; the rhesus macaque is brown or grey in color and has a pink face, bereft of fur. Its tail is of medium length and averages between 22.9 cm. Adult males weigh about 7.7 kg. Females are smaller, averaging 5.3 kg in weight. Rhesus macaques have, on average, their ratio of arm length to leg length is 89%. They have a wide rib cage; the rhesus macaque has 32 teeth with a dental formula of bilophodont molars. The upper molars have four cusps: paracone, metacone and hypocone; the lower molars have four cusps: metaconid, protoconid and entoconid.
Rhesus macaques are native to India, Pakistan, Burma, Afghanistan, southern China, some neighboring areas. They have the widest geographic ranges of any nonhuman primate, occupying a great diversity of altitudes throughout Central and Southeast Asia. Inhabiting arid, open areas, rhesus macaques may be found in grasslands, in mountainous regions up to 2,500 m in elevation, they are regular swimmers. Babies as young as a few days old can swim, adults are known to swim over a half mile between islands, but are found drowned in small groups where their drinking waters lie. Rhesus macaques are noted for their tendency to move from rural to urban areas, coming to rely on handouts or refuse from humans, they adapt well to human presence, form larger troops in human-dominated landscapes than in forests. The southern and the northern distributional limits for rhesus and bonnet macaques currently run parallel to each other in the western part of India, are separated by a large gap in the center, converge on the eastern coast of the peninsula to form a distribution overlap zone.
This overlap region is characterized by the presence of mixed-species troops, with pure troops of both species sometimes occurring in close proximity to one another. The range extension of rhesus macaque – a natural process in some areas, a direct consequence of introduction by humans in other regions – poses grave implications for the endemic and declining populations of bonnet macaques in southern India; the Thai population is locally classified as endangered. There are about 1,000 troops at Wat Tham Pha Mak Ho, Tambon Si Songkhram, Wang Saphung district, Loei province; the name "rhesus" is reminiscent of the mythological king Rhesus of Thrace, a minor character in the Iliad. However, the French naturalist Jean-Baptiste Audebert, who applied the name to the species, stated: "it has no meaning". According to Zimmermann’s first description of 1780, the rhesus macaque is distributed in eastern Afghanistan, Bhutan, as far east as the Brahmaputra Valley in peninsular India and northern Pakistan.
Today, this is known as the Indian rhesus macaque M. m. mulatta, which includes the morphologically similar M. rhesus villosus, described by True in 1894, from Kashmir, M. m. mcmahoni, described by Pocock in 1932 from Kootai, Pakistan. Several Chinese subspecies of rhesus macaques were described between 1867 and 1917; the molecular differences identified among populations, are alone not consistent enough to conclusively define any subspecies. The Chinese subspecies can be divided as follows: M. m. mulatta is found in western and central China, in the south of Yunnan, southwest of Guangxi. M. m. tcheliensis, the north Chinese rhesus macaque, lives in the north of Henan, south of Shanxi, near Beijing. Some consider it as the most endangered subspecies. Others consider it synonymous with M. m. sanctijohannis, if not with M. m. mulatta. M. m. vestita, the Tibetan rhesus macaque, lives in the southeast of Tibet, northwest of Yunnan, including Yushu. M. m. littoralis, the south Chinese rhesus macaque, lives in Fujian, Anhui, Hunan, Guizhou, northwest of Guangdong, north of Guangxi, northeast of Yunnan, east of Sichuan, south of Shaanxi.
M. m. brevicaudus referred to as Pithecus brevicaudus, lives on the Hainan Island and Wanshan Islands in Guangdong, the islands near Hong Kong. M. m. siamica, the Indochinese rhesus macaque, is distributed in Myanmar, in the north of Thailand and Vietnam, in Laos, in the Chinese provinces of Anhui, northwest Guangxi, Hubei, Hunan and eastern Sichuan, western and south-central Yunnan. Around the spring of 1938, a colony of rhesus macaques called "the Nazuris" was released in and around Silver Springs in Florida by a tour boat operator known locally as "Colonel Tooey" to enhance his "Jungle C