The phrase “eats anything” is a biological exaggeration, as no animal can truly digest non-organic matter. The animals people are typically thinking of are highly adaptable dietary generalists and opportunistic feeders. These creatures possess the behavioral and physiological flexibility to exploit a vast range of available food resources, allowing them to thrive in diverse and changing environments worldwide. It is this successful strategy of consuming both plant and animal matter that makes them the ultimate survivors in the natural world.
Defining the “Eats Anything” Concept
The ability to eat “anything” is best understood by combining three specific feeding strategies. An omnivore consumes both plant and animal matter, granting a wider nutritional base than herbivores or carnivores. A dietary generalist can thrive on a wide variety of food types and is not restricted to a narrow ecological niche. The third component is being an opportunistic feeder, a behavioral trait where an animal takes immediate advantage of temporary or unusual food sources, often involving scavenging or exploiting human refuse. The most successful animals that appear to eat everything are those that embody all three characteristics simultaneously.
Top Contenders in the Wild
Several species exemplify this flexible feeding strategy, allowing them to colonize nearly every habitat, including human-dominated urban areas.
The Raccoon (Procyon lotor) is a prime example, with a diet that includes fleshy fruits, nuts, insects, crayfish, eggs, and small vertebrates. They demonstrate an exceptional ability to switch food sources seasonally. Their dexterity allows them to open everything from clams to garbage cans, turning human waste into a reliable food source.
The Brown Rat (Rattus norvegicus) is another master of generalism. Their diet ranges from grains and seeds to chicks, fish, and non-traditional items like soap or beeswax.
Wild Pigs (Sus scrofa) exhibit an aggressive form of opportunistic feeding. While their diet is primarily plant-based (up to 90%), consisting of roots, bulbs, and nuts, the remaining intake includes varied animal matter. This includes earthworms, insects, crustaceans, and the eggs or young of reptiles and birds. Populations have been observed shifting foraging to coastal areas to consume marine invertebrates or preying on fawns or lambs when the chance arises.
Larger generalists, such as the Brown Bear (Ursus arctos), also display this pattern. They consume berries, roots, and grasses in one season and switch to salmon, insects, or large ungulates in another.
Digestive Adaptations for a Broad Diet
The capacity to process diverse food sources requires a digestive system built for compromise rather than specialization. The dentition of generalist omnivores is unspecialized, featuring a mix of teeth types. They possess incisors for biting, canines for tearing meat, and flattened molars for grinding fibrous plant material, effectively combining the tools of both carnivores and herbivores.
The stomach is a single, relatively simple chamber that produces a broad spectrum of enzymes and sufficient acidity to break down both animal protein and plant carbohydrates.
An omnivore’s intestinal tract reflects this intermediate nature, being neither extremely short nor excessively long. The medium-length small intestine facilitates efficient absorption of nutrients from both easily digestible animal matter and complex plant materials. While they lack the specialized fermentation chambers of large herbivores, the large intestine allows for some microbial fermentation of plant fiber. This generalized anatomy ensures metabolic flexibility, allowing the animal to extract adequate nutrition from the environment.
Human Beings: The Ultimate Generalists
Among all species, Homo sapiens stands out as the most successful dietary generalist, largely due to unique cultural and technological adaptations. Early human ancestors expanded their diet through the controlled use of fire, which fundamentally altered food quality. Cooking meat and starchy plant foods, such as tubers, gelatinized the starch, making it far more digestible and increasing the caloric yield. This ability to pre-process food outside the body allowed for a reduction in the size of the human digestive tract over evolutionary time.
The development of food processing techniques, including grinding, fermentation, and drying, further expanded the nutritional landscape. These methods enabled humans to exploit a global pantry of resources that would be indigestible or toxic to other species. This technological capacity, coupled with the ability to transport and store food, has allowed human populations to sustain themselves successfully across every climate and ecosystem on Earth, from the Arctic tundra to the tropical rainforest.