They are distinguished by their tail reduced to a stump, their black face, similar to that of a dog, hairless and surrounded by white hairs, and, in males, by their hairless, purplish-blue buttocks. The ears are black and the fur is grayish brown tinged with olive green. Females, in addition to being smaller, lack color on their buttocks. Its length is about 66 to 70 cm, the weight of the male is around 20 kg, while a female weighs about 12,5 kg.

It has diurnal habits and is semi-terrestrial. It mainly lives on the forest floor, searching through the layer of leaves for food that has fallen from tree species.

Diurnal, arboreal and terrestrial. Males are more terrestrial than females and juveniles. Its gait is quadrupedal.

It has a unimale social system, groups of one male with a group of females, a male can have more than 20 females. Males migrate and may remain solitary.

During the break, the drills engage in the well-known “social facilitation” maneuver: mutual deworming. To encourage his females to do such work, the dominant male lightly touches them on the rump and begins a brief deworming, rummaging through their fur, which has the virtue of stimulating his partner to a task to which he will dedicate much more time and meticulousness. than the male.

They yawn frequently, showing their tremendous canines. Although not a direct threat, yawning seems to serve to underline the power and aggressiveness of the dominant male.

Vocalizations are very common and include a loud “squawk.” It has not been possible to estimate the extent of its residence area, but it is believed that it has a fairly restricted feeding area.