Their long snouts are red and blue and they have yellow-orange beards. They also have colorful rumps, which are thought to aid drills and mandrills in leading their groups through dense forests. These may also provide social and sexual signals. Males are about 40 in. Adult brain weight is 5.6oz.
Mandrills are the largest of all monkeys.
Both drills and mandrills have very short tails. Both have cheek pouches, which enable them to store food to eat later. They are found only in a very small area. Both live in forests and have can have group home ranges ranges of up to 5000ha. Drills have never been seen outside of forests, while mandrills may sometimes venture onto the savanna.