Red colobuses live in large social groups that may typically include between 25 and 40 individuals. Groups usually contain 3–4 adult males and many adult females outnumbering males. An exception to this is when red colobuses co-occur with chimpanzees; ratios of adult males to females tend to be much higher than at sites where chimpanzees are absent, which may have to do with predator protection since chimpanzees prey on red colobus monkeys. Within the groups, males are more permanent members than females, who tend to transfer memberships between groups. As a result, female members of a group are not closely related and do not form bonds with other females.

Males often participate in aggressive interactions with the males of other groups but within their own group, adult males often groom each other. This may be because males in a particular group spend much of their lives with the same fellow male compatriots, and therefore form tight bonds leading to mutual or allogrooming of other males. Allogrooming behavior between females is rarely observed. Some individuals also exhibit food-based feeding competition, wherein individuals compete with other groups by depleting resources such as leaves before others can encounter them.

When under threat by predators, such as chimpanzees, red colobuses engage in long bouts of alarm calling, and males group together to counterattack the chimpanzee hunters that approach the group. The greater the number of red colobus males that counterattack, the less likely a chimpanzee hunt is successful. If the canopy is dense, the males will not attack. Instead, they will retreat quietly along with the other group members to avoid detection. Some red colobus species form strong polyspecific associations with other species such as guenons and follow their range patterns as an anti-predation strategy.