Are Gorillas Omnivores or Herbivores?

Gorillas are overwhelmingly herbivorous, spending most of their feeding time on leaves, stems, bark, and fruit. But they also eat insects, and trace evidence hints they may occasionally consume small vertebrates, which makes calling them strict herbivores a slight oversimplification. In practice, the label that fits best depends on which gorilla population you are talking about and how narrowly you define “herbivore.” The dietary picture across gorilla subspecies is more varied and more interesting than the textbook answer suggests.

What Gorillas Actually Eat Varies by Subspecies

The genus Gorilla includes two species, the eastern gorilla and the western gorilla, each with subspecies that live in quite different habitats and eat quite different things. Mountain gorillas, found in the volcanic highlands of central Africa, are the most strictly plant-eating of the bunch. They rely almost completely on the leaves and stems of herbs and vines that grow year-round at high elevations.¹ Fruit is scarce where they live, so it plays a minor role in their diet. The foods they choose are selective in an unexpected way: toughness matters more than abundance. Mountain gorillas consistently pick the least tough plant parts available, and toughness predicts what they eat better than how common a plant is around them.²

Western lowland gorillas are a different story. Living in tropical lowland forests where fruit trees are plentiful, they eat considerably more fruit. One long-term study at Bai Hokou in the Central African Republic found that these gorillas consumed 239 kinds of foods from 138 species, including the fruits of 77 species. Seeds turned up in 99% of nearly 860 fecal samples.³ They eat fleshy fruit whenever they can get it, but fall back on herbaceous plants and fibrous fruits when ripe fruit is scarce. Western lowland gorillas and mountain gorillas eat foliage throughout the year, but lowland populations eat less of it and more fruit during the wet season.⁴

Dental wear patterns confirm the dietary split. Researchers examining molar surfaces found that Grauer’s gorillas and western lowland gorillas show wear consistent with heavier fruit consumption, while mountain gorilla teeth show the pattern you would expect from a more leaf-based diet.⁵ Gorillas have sharp-cusped molars adapted for shearing fibrous plant material, but that anatomy does not lock them into one food type.

Insects Are a Small but Real Part of the Diet

Here is where the “strict herbivore” label starts to crack. Gorillas eat insects, particularly termites and ants. This is not an accident or a rare curiosity. Molecular analysis of gorilla fecal samples has detected DNA from flies, beetles, moths, mosquitoes, and termites.⁶ Some of these insects are likely ingested incidentally while eating plants, but termite consumption, at least, appears deliberate.

A study comparing insect eating in gorillas and chimpanzees in southeast Cameroon found that gorillas actually ate insects more frequently than chimpanzees did, though chimps consumed larger quantities per feeding bout. The research pointed to something specific: gorillas seemed to select certain termite species, particularly Cubitermes and Thoracotermes, for their nutritional content. Their intake of these termites appeared to meet estimated iron requirements.⁷ In other words, gorillas are not just accidentally swallowing bugs. They seem to be targeting specific insects as a mineral supplement.

Whether eating insects counts as “omnivory” is partly a labeling question. In ecology, omnivores typically eat both plant and animal matter as meaningful components of their diet. Gorilla insect consumption is small in terms of total calories, but it is deliberate, nutritionally targeted, and consistent across populations. Most researchers describe gorillas as primarily herbivorous with minor insectivory, rather than fully omnivorous.

The Vertebrate DNA Mystery

Things get more ambiguous when you move from insects to vertebrates. A molecular study analyzing gorilla fecal samples found DNA from duikers (small forest antelopes) and monkeys in the dung.⁸ The researchers acknowledged the finding was hard to interpret. The DNA appeared in somewhat lower percentages than in bonobo feces, and the study noted that the gorilla population in question had very little observational data available. The gorillas might occasionally consume small vertebrates. Or the DNA could be an artifact: perhaps gorillas ate insects that had fed on vertebrate carcasses, or ingested soil contaminated with vertebrate remains.

Nobody has reliably observed wild gorillas hunting or deliberately eating mammals in the way chimpanzees do. Chimps are well-documented hunters, regularly killing and eating monkeys. Gorillas, by contrast, have no confirmed equivalent behavior. The fecal DNA finding leaves the door open to very occasional vertebrate consumption, but the evidence is far too thin to reclassify gorillas as omnivores on that basis. This is one of those areas where the science is genuinely unresolved, and the honest answer is that we do not know for certain.

How Gorillas Extract Nutrition from Tough Plants

A diet dominated by leaves, stems, and bark creates a digestive challenge. These foods are loaded with cellulose and other structural fibers that gorilla enzymes alone cannot break down. Gorillas rely heavily on microbial fermentation in their enlarged hindgut, essentially outsourcing much of the hard work to the trillions of bacteria living in their intestines.

A multi-omics study of the gorilla gut microbiome found active cellulase and hemicellulase enzymes at work, meaning gut microbes were breaking down cellulose and similar fibers in real time. These fiber-degrading enzymes were especially prominent when researchers looked at which genes were actually being expressed rather than just which genes were present, suggesting the microbes were actively working on tough plant material at the time of sampling.⁹ The same study detected archaeal methanogenic activity, meaning some gut microbes were producing methane as a byproduct of fermentation, much like what happens in cattle.

The microbiome differs between gorilla subspecies in ways that mirror their diets. Mountain gorillas, which eat more fibrous foods, harbor gut bacteria enriched for fiber metabolism. Western lowland gorillas, which eat more fruit, show higher markers associated with simple sugar, lipid, and sterol turnover.¹⁰ The gorilla gut is not a static system; it adjusts its microbial workforce to match what the gorilla is eating. This co-evolution between gorillas and their gut microbes is part of what enables such a fiber-heavy diet to work at all. Researchers have suggested that gorillas likely extract large quantities of energy through fermentation, especially during seasons when they rely on protein-rich leaves rather than fruit.

Seasonal Shifts and Fallback Foods

Gorilla diets are not static across the year. Western lowland gorillas shift substantially between seasons, eating more fruit when it is available and falling back on lower-quality foods when it is not. Group size adds a wrinkle: larger groups of western gorillas showed a stronger link between their fruit consumption and fruit availability, while smaller groups ate relatively more fruit overall regardless of season.¹¹ This suggests that competition within larger groups forces a tighter coupling between what is ripe and what gets eaten.

The concept of “fallback foods” is central to understanding gorilla ecology. When preferred foods like ripe fruit become scarce, gorillas turn to foods that are always available but less nutritionally rewarding: bark, pith, tough leaves, and fibrous roots. These fallback foods, especially barks, are what allow gorillas to form cohesive groups with relatively stable home ranges regardless of how much fruit is around.¹² This is a key ecological difference between gorillas and chimpanzees. Chimps, facing the same fruit scarcity, respond differently: they adjust their ranging patterns or group sizes. Gorillas just eat more of the tough stuff.

Stable isotope analysis of gorilla feces has confirmed these seasonal diet shifts. Researchers found that peaks in certain carbon isotope ratios in feces corresponded to periods of increased fruit feeding, matching what field observers recorded.¹³ This isotope approach offers a way to track dietary changes even in populations that are difficult to observe directly, and it has been particularly useful for studying mountain gorillas whose dense habitat makes direct feeding observation challenging.

A Surprisingly Consistent Nutritional Strategy

Despite eating very different plants, gorilla populations across habitats end up with remarkably similar nutritional profiles in their diets. A comparison of mountain gorillas at two different sites, Bwindi Impenetrable Forest and the Virunga Volcanoes, found that even though the two populations ate different plant species and different plant parts, the overall concentrations of protein, fiber, and carbohydrates were nearly identical. Bwindi gorillas ate diets containing about 18% crude protein and 43% fiber on a dry-matter basis; Virunga gorillas came in at roughly 17% protein and 41% fiber.¹⁴ This finding suggests that gorillas are not just eating what is available. They are selecting foods to hit nutritional targets.

Research into gorilla nutritional strategy has revealed that mountain gorillas prioritize non-protein energy, meaning they aim for a consistent intake of calories from carbohydrates and fats. When fruit is available, they eat it and get plenty of non-protein energy that way. When fruit disappears and leaves dominate the diet, gorillas maintain their energy intake but end up eating surplus protein in the process, because leaves are protein-rich.¹⁵ The upshot is that gorillas over-eat protein rather than under-eat energy. That is a meaningful trade-off, and it helps explain why their diet can swing so dramatically between seasons without obvious health consequences.

How Gorillas and Chimpanzees Split the Forest

Gorillas and chimpanzees share much of their range in central Africa, and how the two species divide up food resources sheds light on gorilla dietary identity. In montane forests where fruit is usually scarce, the dietary split is stark: gorillas rely on leaves and bark while chimpanzees focus on fig fruits.¹⁶ In lowland forests where fruit is more abundant, the two species overlap more in what fruits they eat, but behavioral differences still reduce direct competition.

Chimpanzees are unambiguously omnivorous. They hunt monkeys, eat small mammals, and consume far more animal protein than gorillas. Gorillas’ much heavier reliance on structural plant tissues, their larger body size, their enlarged gut, and their molar anatomy all point to a lineage that diverged from chimpanzees partly by specializing on plant foods that chimps cannot efficiently process. In that evolutionary context, calling gorillas herbivores is broadly correct, even if insects provide a small but targeted nutritional supplement.

What Happens When Zoo Gorillas Eat a Human-Style Diet

The consequences of misunderstanding gorilla dietary needs have played out clearly in captivity. For decades, many zoos fed gorillas calorie-dense, fiber-poor diets that included starchy biscuits and large amounts of fruit. In the wild, western lowland gorillas eat a high-fiber, low-calorie-density diet. The zoo version was essentially the opposite. The result was concerning: many captive gorillas were considered obese, and heart disease became the leading cause of death for adult male gorillas in zoos.¹⁷

When researchers implemented biscuit-free diets low in fruit and high in leafy greens and browse, the results were encouraging. Insulin levels dropped, and cholesterol levels decreased. The dietary change essentially brought captive gorilla nutrition closer to wild conditions, and the gorillas’ metabolic markers improved. This experience reinforces just how fundamentally herbivorous gorillas are. Their physiology is tuned for high-fiber, low-sugar plant foods. Give them the caloric profile of a human diet and their health deteriorates in ways that look a lot like human metabolic syndrome.

More recent research has connected gut microbial metabolites to cardiometabolic disease risk in captive gorillas. Gorillas affected by heart disease showed lower levels of key microbial byproducts like butyrate and propionate, both of which are produced during fiber fermentation.¹⁸ When gorillas do not eat enough fiber, their gut microbes cannot produce these protective compounds. The link between diet, gut microbiome, and heart health in gorillas is a reminder that their herbivorous physiology is not just about what they eat but about an entire ecosystem of microbial partnerships that depend on fibrous plant material to function.

Gorillas as Forest Gardeners

The fruit-heavy diet of western lowland gorillas makes them important seed dispersers. Gorillas eat fruit whole, pass intact seeds through their digestive tract, and deposit them in dung, often at nest sites or along trails. At the Lopé Reserve in Gabon, gorillas removed significant quantities of seeds from multiple tree species and deposited them in conditions favorable for germination.¹⁹ Their nesting habits create concentrated patches of nutrient-rich dung where seeds land with a natural fertilizer boost, and their large body size means they can carry seeds farther from the parent tree than smaller frugivores.

A study of seed dispersal effectiveness in Gabon found that gorillas effectively disperse seeds of numerous plant species, including economically important timber and non-timber forest product species typical of Central African forests.²⁰ Considering the quality of the deposition sites, gorillas play a role in forest dynamics that other dispersers cannot easily fill. As gorilla populations decline, the tree species that depend on them for seed movement face an uncertain future. Losing gorillas does not just mean losing a charismatic species. It means losing a process that shapes the composition of tropical forests.

Medicinal Plants and Cultural Food Processing

Gorillas also consume some plants that appear to have little nutritional value but may serve a medicinal purpose. A range of non-nutritional plant secondary compounds and nutrient-poor bark shows up in great ape diets, and researchers have been building evidence that some of these substances help control parasite infections. Behaviors like bitter pith chewing and leaf swallowing, well-studied in chimpanzees, have also been documented in lowland gorillas.²¹ The evidence for gorilla self-medication is thinner than for chimps, partly because gorillas are harder to observe, but the pattern is consistent enough that it is taken seriously.

Perhaps the most compelling evidence for gorilla food culture comes from studies of nettle processing. Stinging nettles are a common gorilla food, but eating them requires dealing with the stinging hairs. Research on mountain gorillas found that different populations use distinctly different sequences of hand movements to fold and compress nettle leaves before eating them. These processing techniques differed consistently between sites, but individuals within a site used the same method. The best explanation is social transmission: young gorillas learn how to handle nettles by watching others in their group, and the resulting “local traditions” persist across generations.²² Gorillas, in other words, have food culture. They do not just eat plants. They have learned, socially transmitted ways of preparing them.