Drills are sometimes confused with their close relatives, mandrills, which have bright blue and red faces. Drills have shiny black faces instead, with a bright red lower lip that looks a bit like they're smiling all the time. They live in groups of up to 100 monkeys, walking through the forest together looking for food.
They eat almost anything they can find on the forest floor: fruit, seeds, leaves, mushrooms, insects, and small animals. They are most active in the morning and evening, and rest during the hottest part of the day. At night, the whole group climbs up into the trees to sleep, safe from anything walking on the ground.
Drills talk to each other with all kinds of sounds: grunts, screams, and a 'crowing' call that sounds a bit like a rooster. The leader of the group is a big male, and he uses his face and voice to keep the family together as they walk through the thick forest where they cannot always see each other.
Because drills only live in such a small area, they are one of Africa's most endangered monkeys. Conservation groups in Nigeria run special projects in Cross River State, in the southeast of the country, where most wild drills live - protecting the forest so the drill families can keep finding food and a safe place to sleep.