Carnivores: Facts About Meat Eaters

A carnivore is an animal or plant that eats the flesh of animals. Most, but not all, carnivorous animals are members of the Carnivora order; but, not all members of the Carnivora order are carnivorous. 

"A carnivore is simply any species that eats meat, and this can range from carnivorous plants and insects to what we typically think of when we hear the word carnivore, like tigers or wolves," said Kyle McCarthy, an assistant professor of wildlife ecology in the University of Delaware's College of Agriculture and Natural Resources.

Carnivora — or "flesh devourers," in Latin — is an order of placental mammals that includes canids such as wolves and dogs, felids (cats), ursids (bears), mustelids (weasels), procyonids (raccoons), pinnipeds (seals) and others, according to Encyclopedia Britannica. The order consists of 12 families and 270 species in all.

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While some carnivores eat only meat, other carnivores also supplement their diets with vegetation on occasion. For example, most bears are omnivores, which means they eat both plants and meat, McCarthy explained.

Carnivorous plants

Animals aren't the only carnivores — there are more than 600 species of carnivorous plants, according to the Botanical Society of America. These plants get at least some of their nutrients by trapping and digesting insects and sometimes even small frogs and mammals. Because the most common prey for most carnivorous plants are insects, these leafy flesh-eaters are also called insectivorous plants. 

While most plants absorb nitrogen from the soil through their roots, carnivorous plants get nitrogen from animal prey that gets trapped in their modified leaves. The traps work in various ways. A Venus flytrap (Dionea muscipula), for example, has hinged leaves that snap shut when trigger hairs are touched. A pitcher plant has a pitfall trap; its leaves fold into deep pits filled with digestive enzymes. And sundews and butterworts have sticky mucus on their stalks that stops insects in their tracks.

Carnivore types

There are three different categories of carnivores based on the level of meat consumption: hypercarnivores, mesocarnivores and hypocarnivores.

Carnivores that eat mostly meat are called hypercarnivores. These creatures are considered obligate carnivores because they cannot properly digest vegetation and have a diet that consists of at least 70 percent meat, according to National Geographic. The cat family, including lions, tigers and small cats, for example, are obligate carnivores, as are snakes, lizards and most amphibians.

Many hypercarnivores, including some members of the Carnivora order, have heavy skulls with strong facial musculature to aid in holding prey, cutting flesh or grinding bones. Many also have a special fourth upper molar and first lower molar. "They close together in a shearing action, like scissors, which allows [the] animals to slice meat from their prey," said McCarthy. These two teeth together are called the carnassial teeth.

A rare example of a hypercarnivore that does not have carnassial teeth is the crabeater seal. It has teeth that strains tiny zooplankton such as krill from the water, according to the University of Michigan's Animal Diversity Web (ADW). Carnivorous baleen whales, which have no teeth at all, use a similar strategy to strain krill from sea water. Their mouths contain rows of strong, flexible baleen plates made of keratin, the same protein that's in human fingernails.

Animals that depend on meat for at least 50 percent of their diet are called mesocarnivores. Along with meat, these animals will also eat fruits, vegetables and fungi. Mesocarnivores are typically small to mid-size species and often live close to human populations. Raccoons, foxes and coyotes are examples of mesocarnivores.

Hypocarnivores are carnivores that eat the least amount of meat — less than 30 percent of their diet, according to National Geographic. These animals, which can also be considered omnivores, eat fish, berries, nuts and roots, as well as meat.

Size

The world's largest animal is also the world's largest carnivore. The blue whale (Balaenoptera musculus) grows up to 100 feet (30 meters) long and weighs up to 200 tons (180 metric tons). The largest carnivore on land is the polar bear, which can weigh 800 to 1,300 lbs. (363 to 590 kilograms), and can grow to 9 feet long (3 m) from nose to tail, according to World Wildlife Fund. The smallest carnivorous mammal is the least weasel. It grows no more than 16 inches long (40.6 centimeters) and weighs about 7 ounces (198 grams). 

Characteristics of carnivores

Though carnivores come in many shapes and sizes, they share a few similarities. Most carnivores have relatively large brains and high levels of intelligence. They also have less complicated digestive systems than herbivores. For example, many herbivores have multiple stomachs, while carnivores only have one, according to Encyclopedia Britannica. 

Though all carnivores eat meat at some level, the frequency of their feeding can vary. Warm-blooded carnivores tend to burn a lot of calories. Because of this, they have to hunt and eat often to keep to keep up their energy levels. Cold-blooded carnivores, on the other hand, use fewer calories and can rest days or even months between meals. 

Carnivores as part of the food web

Carnivores sit at the third trophic level in the food web, along with omnivores. Carnivores eat other carnivores, as well as herbivores and omnivores, depending on their species, according to National Geographic. 

As the top tier of the food web, carnivores keep the populations of other animals in check. If a carnivore population is wiped out by disease, natural disasters, human intervention or other factors, an area can experience an overpopulation of other creatures lower in the food chain.

Sometimes, carnivores will be brought into an area to help with overpopulation of herbivores. For example, wolves were reintroduced to Yellowstone National Park in 1995 — after being eradicated from the region 70 years earlier — to help reduce the elk population. Eventually, this reintroduction allowed woody plants to recover from the consumption of too many elk, according to the University of Michigan. 

Further reading:

• Oxford Journals: The Ecological Role of the Mammalian Mesocarnivore
• U.S. Forest Service: The Status and Conservation of Mesocarnivores in the Sierra Nevada
• Wildlife Conservation Society: Mesocarnivores of Northeastern North America

This article was updated on Dec. 4, 2018 by Live Science Senior Writer, Mindy Weisberger.