The blue monkey or diademed monkey (Cercopithecus mitis) is a species of guenon native to various parts of east, central and southern Africa. This also includes the Congo River basin.
Despite its name, the blue monkey is not noticeably blue. It has little hair on its face, and this does sometimes give a blue appearance. It never has the vivid blue appearance of a mandrill. The fur is short, and mainly a grizzled brown color apart from the face. The face is dark with a pale yellowish patch on forehead. The mantle varies between subspecies. Typical sizes are from 19.69 to 25.6 inches (50 to 65 cm) long. The females weigh a little over 8.82 lbs (4 kg) and males up to 17.64 lbs (8 kg). The tail is almost as long as the rest of the animal.
The blue monkey is found in rain forests and mountain bamboo forests. It lives largely in the forest canopy, coming to the ground infrequently. It is very dependent on humid, shady areas with plenty of water. It eats mainly fruit and leaves, but will take some slower-moving invertebrates. It prefers to live in tall trees that provide both food and shelter. They are suffering from the loss of its natural habitat.
The mating system has more than one mate. Females normally give birth every two years. They give birth during the onset of the warm, rainy season. Gestation is around 5 months and the infants are born with fur and with their eyes open. Group sizes range from 10 to 40, containing only a single adult male. It is often found in groups with other species of monkeys such as the red-tailed monkey and various red colobus monkeys.