Definition of Omnivore

Flatback sea turtle - an example of an omnivore.
Flatback sea turtle hatchling. Flatback turtles are omnivores that feed on invertebrates and seaweed. Doug Perrine/Photolibrary/Getty Images

An omnivore is an organism that eats both animals and plants. An animal with such a diet is said to be "omnivorous."

An omnivore that you're probably pretty familiar with are humans - most humans (other than those who don't get any nutrition from animal products) are omnivores. You can read on for more examples of omnivores.

The Term Omnivore

The word omnivore comes from the Latin words omni "all" and vorare, meaning "devour, or swallow" - so, omnivore means "devours all." This is pretty accurate, as omnivores can get their food from a variety of sources.

Food sources can include algae, plants, fungi and animals.   Animals may be omnivorous their entire lives, or at different stages (such as some sea turtles, see below). 

Advantages and Disadvantages of Being an Omnivore

Omnivores have the advantage of being able to find food in a variety of places. Therefore, if one prey source diminishes, they can fairly easily switch to another one.  Some omnivores are also scavengers, meaning they feed on dead animals or plants, which further increases their food options.

They do have to find their food - omnivores either wait for their food to pass by them or need to actively seek it out.  Since they have such a general diet, their means of getting food is not as specialized as carnivores or herbivores. For example, carnivores have sharp teeth for ripping and gripping prey, and herbivores have flatter teeth adapted for grinding.  Omnivores may have a mix of both kinds of teeth (think of our molars and incisors as an example).

A disadvantage for other marine life is that marine omnivores may be more likely to invade non-native habitats. This has cascading effects on native species, which may be preyed-upon or displaced by the invading omnivore. An example of this is the Asian shore crab, which is native to countries in the Northwest Pacific Ocean, but was transported to Europe and the U.S., and is out-competing native species for food and habitat.

Examples of Marine Omnivores

Below are some examples of marine omnivores:

  • Many crab species (including blue, ghost and Asian shore crabs)
  • Horseshoe crabs
  • Lobsters (e.g., American lobster, spiny lobster)
  • Some sea turtles - Olive ridley and flatback turtles are omnivores. Green turtles are herbivores as adults, but omnivores as hatchlings. Loggerhead turtles are carnivores as adults but omnivores as hatchlings.
  • Common perwinkle - these small snails feed mostly on algae but may also eat small animals (e.g., barnacle larvae).
  • Some types of zooplankton
  • Sharks are generally carnivores, although the whale shark and basking shark may be considered omnivores, as they are filter feeders that eat plankton. As they mow through the ocean with their enormous mouths open, the plankton they consume may include both plants and animals. Using that line of reasoning, mussels and barnacles may be considered omnivores, since they filter small organisms (which may contain both phytoplankton and zooplankton) from the water. 

Omnivores and Trophic Levels

In the marine (and terrestrial) world, there are producers and consumers. Producers (or autotrophs) are organisms that make their own food. These organisms include plants, algae and some types of bacteria.

Producers are at the base of a food chain.  Consumers (heterotrophs) are organisms that need to consume other organisms to survive. All animals, including omnivores, are consumers. 

In a food chain, there are trophic levels, which are the feeding levels of animals and plants. The first trophic level includes the producers, because they produce the food that fuels the rest of the food chain. The second trophic level includes the herbivores, which eat producers.  The third trophic level includes omnivores and carnivores.

References and Further Information:

  • Chiras, D.D. 1993. Biology: The Web of Life. West Publishing Company.
  • Harper, D. Omnivorous. Online Etymology Dictionary. Accessed September 29, 2015.
  • National Geographic. Autotroph. Accessed September 29, 2015.
  • The Oceanic Society. What Do Sea Turtles Eat? Accessed September 29, 2015.