August 27, 2026 a crazy-looking animal. source. This is part II of a series discussing the largest monkey species, mandrills and drills. Part one covered mandrills. This post will cover drills. Drills (Mandrillus leucophaeus) are closely related to mandrills, as they are in the same genus (Mandrillus) and the same family Cercopithecidae. Drills live in similar areas as the mandrill, being restricted to western Africa in Nigeria, Cameroon, and Equatorial Guinea. As the wikipedia points out, the entire species' range is about the size of the state of West Virginia. We think there's about 4,000 total individuals left, so they are accordingly listed as nationally endangered. Drills are threatened mostly by habitat loss due to human encroachment and they have a lot of hunting pressure. An IUCN report from 2008 indicates that their population has declined more than 50% over the past 3 decades. People hunt them with dogs sometimes, and this tends to result in mass casualties. There is a very big demand for bushmeat (meat from wildlife) in the region. Mandrills have brown fur over most of their bodies, short tails, and black faces with a rim of white fur outlining the face. They are active during the day, omnivorous, and social. Missing the rainbow: Drills also have two sexes that are very distinct from one another, but don't reach the extremity that mandrills do - they didn't eat enough skittles, so they lack the rainbow. Males are definitely bigger and larger, often weighing more than twice that of females. Males on average are about 70 lbs (32.3 kg). They do have the larger muzzle with swelling and ridges on the sides, but their faces are almost entirely black skin, so they look very striking. The muzzle ridges are influence by circulating androgen (a hormone), so it serves as a reproductive signal. These visual signals are mostly likely to signal to other males what an individual's status is. Males will avoid fighting another male if that male is clearly stronger and more dominant than them. Females seem to not have a preference for any of the males' coloration, so it may be strictly for a male-male signal. Males do have the larger canine teeth also, reaching almost 2 inches (4.5 cm) in length. Males do have a little bit of color! They have bright red patches on the chin, and their rear areas have swirls of color in red, blue, and white. Females lack the red chin but do have red colors around the groin area, especially during mating season. As with mandrills, these signals are probably pretty useful when you live in big groups because it tells you immediately who is ready for mating, who is dominant, who is too big to fight, etc. Other biology: Like a lot of monkeys, they are really omnivorous and eat a bit of everything with a focus on fruits. As a result they are big seed dispersers. They sometimes eat leaves and grasses too. They spend a lot of time on the ground but are also good climbers. At night, drills seek protection in the trees, which they will also run to in the case of danger or a predator. Like most monkeys in Africa, they are preyed upon by the leopard. Drills usually do not congregate in the giant hordes that mandrills do, and instead are in groups of 15-75 individuals of mixed sexes. There are many fewer males in each group compared to females. Troops are mainly made up of related females and their offspring, with a small number of dominant males present. Males exhibit a strict social hierarchy and control access to females, with a dominant male preventing other males from entering or mating. Despite the smaller groupings, occasionally drills have been recorded in really big groups of about 100 individuals. It still doesn't reach anything like the 500+ groups mandrills are usually found in. I wonder why? look at this babby. females are much smaller than males. source. Island monkeys: Interestingly, drills are also found on an island off the coast of Equatorial Guinea, called Bioko Island. On the island, this species exists across a range of elevations, from 0 meters above sea level up to 1000 meters. Not surprisingly, their diets across the elevational range can vary a lot, with lowland drills eating a lot of fruits while montane ones focus more on leaves and stems of plants. In contrast, mandrills are almost always found at low elevations. On Bioko Island, drills were also found to eat crabs sometimes (living that island life), and sometimes arthropods like millipedes, ants, or termites. In the mountains there, drills also ate mushrooms, which is pretty rare in primate diets. It's difficult for a lot of animals to eat fungi because it usually requires specialized digestion in order to break it down. Basically, there are very few studies on drills and we don't know much about them. Like mandrills, they are difficult to study because they live in dense forest habitats, making observational studies nearly impossible. Drills are far less studied than mandrills for some reason, maybe because they are rarer. Apparently there are some dog-like creatures in the Hunger Games series that were inspired by mandrills and drills. Other than this, I'm not aware of any media or popular culture representations of drills. More information: BBC - Primates: a documentary about various primate species, with the drills included. BBC iPlayer is available in the UK to watch for free I think, but I don't have access to it in the US. Monkeys of Bioko documentary - available through Paramount+ and the Smithsonian Channel in the US. 4 minutes of the documentary can be viewed here. The Drill Project - short documentary (40 min) An introduction to drills and footage in their natural habitat on Bioko Island. Even if you skip through parts of this, I would recommend watching it because drills are so strange looking, it's weird to see them moving around even. Their dark faces are like they are wearing masks. Also there's cute footage of baby drills (I'm calling them drillets). Sources: Owens, Jacob R., et al. "From frugivore to folivore: Altitudinal variations in the diet and feeding ecology of the Bioko Island drill (Mandrillus leucophaeus poensis)." American Journal of Primatology 77.12 (2015): 1263-1275. The Drill Project Wikipedia - Drill