Rhesus Monkey , macaque found throughout India and Nepal, eastern Afghanistan, and northeastern China and Indochina, and held sacred by the Hindus. It is partly migratory, sometimes ascending the Himalayas to an altitude of about 2500 m (about 8200 ft) in summer. An adult rhesus has a stoutly built body that may be up to 63 cm (25 in) long, with a tail half that length. The skin hangs in loose folds about the neck, breast, and abdomen. The silky hair is yellowish brown, the naked skin is brown to yellowish-brown, and the large posterior callosities are bright red. The monkeys live in troops of 8 to 180 individuals. The young are readily tamed and have been used in menageries and circuses and as "organ-grinders' monkeys," but their dispositions worsen with age. In recent years the rhesus monkey has been viewed by humans as an agricultural pest, largely due to food shortages in India. This intolerance of the monkeys has led to their decline in agricultural areas and villages. Because they are physiologically similar to humans, rhesus monkeys have been used as research animals to an extent that has greatly reduced their population; India now bars their exportation. The monkeys have been used extensively in research on human blood chemistry, and the Rh factor in blood derives its name from them. Psychological studies carried out on the animals have aided in the understanding of infant-mother relationships in humans, and rhesus monkeys were launched in high-altitude tests of rockets following World War II .