Omnivores span every major branch of the animal kingdom, from mammals and birds to reptiles, fish, crustaceans, and insects. The list is far longer than the usual suspects of bears, pigs, and raccoons. Many animals that people assume are strict carnivores or herbivores actually eat a mix of plant and animal material, and some switch their diet dramatically depending on the season, their age, or what food happens to be available. What makes an omnivore is less about a fixed menu and more about flexibility.
Mammalian Omnivores
Bears are probably the most recognizable omnivores on Earth, and brown bears illustrate the lifestyle well. In Scandinavia, brown bear diets swing heavily with the seasons: berries, fungi, and green plant matter dominate at different times of year, while insects and vertebrate prey make significant contributions that vary from one year to the next.1Wildlife Biology. Seasonal and annual variation in the diet of brown bears Ursus arctos in the boreal forest of southcentral Sweden Geography matters too. When researchers compared brown bear diets across central and northern Europe, the proportion of animal prey in the diet rose with latitude, meaning bears in the far north eat more meat than their southern relatives.2Annales Zoologici Fennici. Carnivory is Positively Correlated with Latitude among Omnivorous Mammals: Evidence from Brown Bears, Badgers and Pine Martens That same pattern held for badgers and pine martens, suggesting it reflects a broad ecological pressure rather than something unique to bears.
Wild boar are textbook omnivores. Across western Europe, their diet includes mast (acorns, beechnuts), roots, green vegetation, and agricultural crops, along with animal material like invertebrates and small vertebrates. The striking breadth of their food habits, shifting with season, region, and local availability, marks them as opportunistic omnivores whose menu at any given time is driven mostly by what is around.3Mammal Review. Diet of wild boar Sus scrofa in Western Europe, with particular reference to consumption of agricultural crops Domestic pigs descend from wild boar and retain this same flexible appetite, which is one reason they adapt so easily to varied farming conditions worldwide.
Raccoons and opossums are familiar North American omnivores. Both are well documented eating everything from fruits, berries, and nuts to insects, earthworms, small vertebrates, and garbage. Their willingness to eat almost anything edible is a major reason both species thrive alongside humans.4Oxford Academic / Journal of Mammalogy. Earthworms in the Winter Diet of the Opossum and Raccoon
Primates are more omnivorous than many people realize. Vertebrate meat-eating has been documented across at least 12 primate families, 39 genera, and 89 species. Chimpanzees are the most famous primate hunters, but capuchins, baboons, bonobos, blue monkeys, and squirrel monkeys all eat vertebrate prey with some regularity. That said, meat usually makes up only a small share of total feeding time and energy intake for most primates. The strongest current hypothesis is that meat provides micronutrients that are hard to get from plant foods alone, rather than serving mainly as an energy or protein source.5PubMed. Meat eating by nonhuman primates: A review and synthesis
Other well-known mammalian omnivores include skunks, hedgehogs, coatis, most species of mice and rats, many squirrel species, and the domestic dog. Coyotes deserve special mention: in summer, pulses of white-tailed deer fawns and blackberries made up over half their diet in one study, while persimmon fruits became important in fall.6PubMed Central. Resource pulses shape seasonal and individual variation in the diet of an omnivorous carnivore That seasonal swing is characteristic of how many mammalian omnivores operate: they follow whatever food pulse the environment offers.
Birds That Are Omnivores
Chickens and turkeys are commonly called grain-eaters, but that label is misleading. Their wild ancestors and free-ranging relatives eat a wide variety of plant and animal foods, and seeds are not often a primary component. Jungle fowl chicks and wild turkey poults get over half their diet from insects, and adult females ramp up insect consumption around the time of reproduction.7Journal of Applied Poultry Research. Informal Nutrition Symposium Poultry Nutrition: A Comparative Approach Classifying chickens as granivores misrepresents their digestive anatomy and nutritional strategy. They are omnivores, full stop.
The common raven is another clear omnivore. It scavenges carcasses and human garbage, hunts rodents, raids nests for nestlings, and consumes large numbers of arthropods including scorpions and grasshoppers. Ravens also sometimes eat large amounts of seeds and grains.8Birds of the World. Common Raven (Corvus corax) Crows, jays, magpies, and most other corvids share this flexible diet. Beyond the corvid family, omnivory is common in gulls, starlings, emus, cassowaries, rheas, many ducks and geese, and a long list of songbirds that supplement seed diets with insects and spiders.
Reptiles and Amphibians
Omnivory might seem unusual for reptiles, but it is well-documented in several groups. Freshwater turtles in the family Emydidae, including the familiar red-eared slider, undergo a dramatic dietary shift as they grow. Juveniles eat mainly animal prey, then transition to a more plant-heavy diet as adults.9PubMed. Response to dietary dilution in an omnivorous freshwater turtle: implications for ontogenetic dietary shifts The long-standing explanation was that small turtles simply cannot process enough plant material to meet their energy needs, but experiments with yellow-bellied sliders showed that even small turtles can compensate for low-quality diets by eating more, suggesting the shift is not purely about gut capacity.10PubMed. Ontogenetic diet shifts and digestive constraints in the omnivorous freshwater turtle Trachemys scripta The real reasons juveniles prefer animal prey remain an active research question.
Bearded dragons, popular as pets, are omnivorous in the wild too. Free-roaming Australian central bearded dragons get roughly 61% of their dry matter intake from animal material, mostly arthropods, with termite alates making up the bulk. Plant material contributes about 16% of their intake.11PubMed. The diet of free-roaming Australian Central Bearded Dragons (Pogona vitticeps) That mix of bugs and vegetation is what captive diets should try to approximate, though many pet owners over-rely on leafy greens and underestimate how insect-heavy the natural diet actually is.
Other omnivorous reptiles include box turtles, many skink species, and some iguanids. Among amphibians, true omnivory is rarer, but certain frog species supplement insect diets with plant matter, and some tadpoles are opportunistic omnivores that eat algae, detritus, and small animal matter interchangeably.
Fish and Crustaceans
Many freshwater and marine fish are omnivores. The red-bellied pacu, a relative of piranhas native to South America and introduced widely around the tropics, feeds on a mix of fish remains, aquatic plants, terrestrial plant material, and fruits and seeds.12Neotropical Ichthyology. Diet shift of Red Belly Pacu Piaractus brachypomus (Cuvier, 1818) (Characiformes: Serrasalmidae), a Neotropical fish, in the Sepik-Ramu River Basin, Papua New Guinea Juvenile pacu in Papua New Guinea, where they were introduced, consumed 28 different food items across 11 broad categories. Other well-known omnivorous fish include catfish, carp, tilapia, piranha (yes, many piranha species eat fruit and seeds), and most cichlids.
Crustaceans are some of the most successful omnivores in aquatic ecosystems. The invasive Chinese mitten crab and signal crayfish both eat a wide, overlapping range of foods including aquatic plants, algae, land-based detritus, invertebrates, and fish.13Freshwater Biology. Feeding behaviour, predatory functional responses and trophic interactions of the invasive Chinese mitten crab (Eriocheir sinensis) and signal crayfish (Pacifastacus leniusculus) The red swamp crayfish, one of the most invasive freshwater animals on the planet, takes this flexibility even further. When aquatic food runs low, it directly accesses terrestrial vegetation, venturing onto land to eat plant material in a way that helps the population survive resource crunches.14PLoS ONE. ‘Leaves and Eats Shoots’: Direct Terrestrial Feeding Can Supplement Invasive Red Swamp Crayfish in Times of Need The Australian redclaw crayfish, commonly farmed in aquaculture, can digest both plant and animal ingredients, though it handles carbohydrates from plant sources more efficiently than those from animal sources.15Aquaculture Nutrition. Carbohydrate and lipid digestibility of animal and vegetal ingredients and diets for juvenile Australian redclaw crayfish, Cherax quadricarinatus
Insects and Other Invertebrates
Omnivory is extremely common among insects. Crickets, cockroaches, ants, wasps, earwigs, and many beetle species eat both plant and animal food. Field research in Uruguay tested five co-existing species of predators and omnivorous scavengers, including two cricket species, two cockroach species, and a harvestman (a relative of spiders). Some were limited by total food availability, while one cockroach was limited specifically by non-protein nutrients like lipids, pointing to how differently omnivory works even among species sharing the same habitat.16Ecological Entomology. Contrasting patterns of food and macronutrient limitation in the field among co‐existing omnivorous carnivores
Ants may be the most ecologically important invertebrate omnivores. Fire ants, carpenter ants, and Argentine ants eat seeds, nectar, fungi, other insects, and scavenged animal tissue. Many ant species farm aphids for honeydew while simultaneously hunting other insects, making them both herbivore-associates and active predators. Social wasps like yellowjackets follow a similar pattern, feeding larvae on chewed-up insects while adults consume sugary plant nectar and fruit.
How Gut Design Reflects a Mixed Diet
Omnivores generally have digestive systems that sit between the extremes of specialist herbivores and carnivores. Their intestines tend to be intermediate in length and complexity, their stomachs produce moderate levels of acid, and their teeth (in mammals) often combine features for cutting and grinding. In murine rodents, tooth shape reliably reflects diet: species eating plant-dominated diets tend to have broad, robust incisors for handling abrasive plant material, while species eating mainly animal prey have thinner, narrower incisors suited for piercing and cutting.17Biological Journal of the Linnean Society. Dietary adaptations in the teeth of murine rodents Muridae: a test of biomechanical predictions Omnivorous rodents had larger incisors than expected, possibly due to their typically larger body sizes.
At the molecular level, digestive capacity tends to match dietary load. Across both vertebrates and invertebrates, natural selection has tuned the gut’s enzyme production and nutrient transport so that digestive capacity roughly matches what the animal typically eats, with only a modest surplus.18PubMed. Ecological physiology of diet and digestive systems When the diet changes, many animals can adjust enzyme levels and transporter activity in response. This flexibility in gut physiology is part of what allows omnivores to thrive on shifting food supplies. The gut microbiome also plays a role: across animals in the wild, microbial composition and functional capacity are strongly associated with diet, alongside factors like taxonomy and social structure.19Science. Diversity and functional landscapes in the microbiota of animals in the wild
Why Omnivory Evolves So Often
Omnivory is not just a quirk of a few species. It evolves repeatedly across the tree of life, and the evolutionary dynamics behind it are revealing. Among mammals, the fastest dietary transitions are into omnivory from both herbivory and carnivory, while direct transitions between strict herbivory and strict carnivory are vanishingly rare.20PubMed Central. Tempo of trophic evolution and its impact on mammalian diversification In other words, omnivory acts as a bridge. When an herbivore lineage starts eating animal prey, or a carnivore lineage starts eating plants, both pass through an omnivorous stage.
A more recent analysis of terrestrial mammal diets reinforced this pattern and added nuance. Transitions between herbivory, invertebrate-eating, and vertebrate-eating are nearly nonexistent unless they pass through omnivorous or mixed-feeding intermediates. The transition rate from omnivory to herbivory was the highest of all dietary shifts measured.21PubMed Central. What is a mammalian omnivore? Insights into terrestrial mammalian diet diversity, body mass and evolution Omnivory, in this view, is less of a permanent destination and more of a revolving door that lineages pass through on their way to specialization. That does not make it unstable in individual species; bears, pigs, and raccoons have been omnivores for millions of years. But across evolutionary time, omnivore lineages tend to generate fewer descendant species than specialist herbivore or carnivore lineages do, because specialists can subdivide their niche more finely.20PubMed Central. Tempo of trophic evolution and its impact on mammalian diversification
What Omnivory Does for Ecosystems
Ecologists used to assume that omnivory destabilized food webs, because feeding at multiple levels muddied the tidy predator-prey chains that mathematical models handled well. The evidence now points the other direction. Experimental work has shown that increasing the degree of omnivory in a community actually stabilized its dynamics.22PubMed. Omnivory as a stabilizing feature of natural communities A broader synthesis found that omnivory stabilizes food webs under several common conditions: when it occurs as a life-history shift (juveniles eating different food than adults), when prey have refuges or defenses that reduce predation pressure, and when omnivores compete with or interfere with each other.23Ecosphere. Stability and persistence of food webs with omnivory: Is there a general pattern? The upshot is that omnivores act as buffers. When one food source crashes, they switch to another, dampening the kind of boom-bust cycles that can cascade through simpler food chains.
Omnivores in Cities
Urbanization creates conditions that strongly favor omnivores. Cities concentrate food resources in predictable locations (trash bins, pet food dishes, bird feeders, dumpsters), and the species best equipped to exploit those resources are the ones with flexible diets. Synanthropic species, those that live alongside humans, commonly rely on anthropogenic food subsidies, and this reliance shapes urban food webs in ways ecologists are still working to understand.24Functional Ecology. Trophic structure in a rapidly urbanizing planet
Rats offer a vivid case study. Analysis of rat bones from historical urban sites in Upper Canada showed that urban rats consistently had higher-protein, less-variable diets than their rural counterparts, with regular access to animal protein sources. Their dietary signatures were remarkably uniform compared to rats from rural and wild settings.25PubMed Central. Urban rats have less variable, higher protein diets That is a counterintuitive finding: you might expect cities to force animals into nutritional stress, but for omnivores capable of exploiting human waste, cities can actually provide a richer, more reliable food supply than the wild. This dietary security is one reason raccoons, crows, gulls, foxes, and coyotes have expanded into urban environments so successfully. The flexibility that defines omnivory turns out to be the ideal toolkit for life in a human-dominated landscape.
Animals Often Misclassified
The line between omnivore and specialist is blurrier than textbooks suggest, and several animals are routinely placed in the wrong category. Chickens and turkeys, as noted above, are called granivores in many references despite having the anatomy, food preferences, and nutritional strategies of omnivores.7Journal of Applied Poultry Research. Informal Nutrition Symposium Poultry Nutrition: A Comparative Approach Deer are typically considered strict herbivores, but trail camera footage and field studies have caught white-tailed deer eating nestling birds, and similar occasional meat-eating is documented in cattle, sheep, and horses. These events are rare enough that calling deer omnivores would be misleading, but they underscore that obligate herbivory is less absolute than it appears.
Hippos are another surprising case. Long assumed to be pure herbivores, they have been observed eating meat and carcasses on multiple occasions, though how nutritionally meaningful this behavior is remains debated. On the other end, many animals classified as carnivores eat more plant material than their reputation suggests. Red foxes eat substantial amounts of fruit. Wolves in some regions eat blueberries seasonally. Even domestic cats, which are obligate carnivores physiologically, will eat grass and certain plant matter, though they cannot derive much nutrition from it. The classification system works as a rough guide, but individual diets exist on a spectrum, and many species hover near the edges of their assigned category.
A Quick Reference List
Because this article’s title promises a comprehensive list, here is a grouped summary of well-documented omnivores across major animal groups. This is not exhaustive but covers the species and groups most commonly encountered or asked about.
- Bears: Brown bears, black bears, sun bears, sloth bears, and spectacled bears all eat significant quantities of both plant and animal food. Polar bears and giant pandas are the exceptions, sitting at the carnivore and herbivore ends respectively.
- Pigs and peccaries: Wild boar, domestic pigs, warthogs, bushpigs, and all three peccary species.
- Primates: Chimpanzees, bonobos, baboons, capuchins, squirrel monkeys, blue monkeys, marmosets, tamarins, macaques, and humans.
- Other mammals: Raccoons, opossums, skunks, coatis, hedgehogs, badgers, coyotes, foxes (most species), most mice and rats, many squirrel species, and domestic dogs.
- Birds: Crows, ravens, jays, magpies, chickens, turkeys, emus, cassowaries, rheas, gulls, starlings, grackles, robins, and most ducks and geese.
- Reptiles: Box turtles, red-eared sliders, other emydid turtles, bearded dragons, blue-tongued skinks, and some tegus.
- Fish: Pacu, carp, catfish (many species), tilapia, piranha (several species), most cichlids, and many minnow species.
- Crustaceans: Most crayfish species, many crab species including the Chinese mitten crab, and many shrimp.
- Insects and arachnids: Crickets, cockroaches, ants (most species), social wasps, earwigs, many beetles, and harvestmen.
The animals on this list share a common thread: their guts, teeth, and behavior allow them to switch between food sources as availability changes. That flexibility comes with a trade-off. Omnivores are rarely the most efficient at digesting any single food type. A ruminant extracts more energy from grass than a bear ever could, and a hawk processes a mouse more efficiently than a crow does. But when the grass dries up or the mice disappear, the specialist is stuck and the omnivore finds something else to eat. That trade-off between efficiency and resilience is the defining bargain of the omnivorous lifestyle.