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What is the Most Numerous Animal?

Michael Anissimov
Updated May 21, 2024
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When asked what the world's most numerous animal is, most people assume the insects. The Entomological Society of America claims insects are 1.6 billion times more numerous than humans, in which case there would be about 1019 insects. However, insects, although they are the most diverse animals (with over a million species described by science), are not the most numerous animals — they're too large, usually measuring in the millimeters or centimeters. To find the most numerous animal, we must zoom in to a smaller scale.

Mites, a form of arachnid, not an insect, are ubiquitous in practically every environment, and are often considered one of the most numerous animals on the planet. Like insects, mites are thought to contain over a million different species, but this is even more impressive than in the case of insects. This is because mites (Acarina) are just a subclass of organism, while insects (Insecta) are a Class, a higher taxonomic division. Mites have a smaller average size, around a millimeter millimeters. This tiny size, along with their fast reproductive rates and ubiquitous range, makes it reasonable to estimate that mites outnumber insects at least 10:1. If so, there are more than 1020 mites on Earth.

There are organisms even more numerous than both mites and insects. These include various species of microfauna, most notably the nematodes, also known as roundworms. Nematodes are very small (many have about 1000 cells, and measure 1-2 mm in length) and very numerous. They cover practically every square inch of the land and sea. Nematodes account for 90% of all life on the ocean floor. In certain fertile areas of topsoil, there are over a trillion nematodes per square mile. Most biologists agree that nematodes are both the most ubiquitous and most numerous animal on Earth. It is reasonable to estimate that nematodes outnumber mites 10:1, and probably greater than 100:1. If so, then there are 1021 - 1022 nematodes on Earth, making them the most numerous animal.

All The Science is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Michael Anissimov
By Michael Anissimov , Writer
Michael Anissimov is a dedicated All The Science contributor and brings his expertise in paleontology, physics, biology, astronomy, chemistry, and futurism to his articles. An avid blogger, Michael is deeply passionate about stem cell research, regenerative medicine, and life extension therapies. His professional experience includes work with the Methuselah Foundation, Singularity Institute for Artificial Intelligence, and Lifeboat Foundation, further showcasing his commitment to scientific advancement.

Discussion Comments

By anon145821 — On Jan 24, 2011

Bacteria are not in the animal kingdom.

Fish are the most numerous vertebrate. There is still debate about the most numerous fish species.

By anon114651 — On Sep 29, 2010

anon109496 - the article is about the most numerous animal, not the most numerous organism.

By anon109496 — On Sep 07, 2010

Interesting article, but dead wrong.

Bacteria is the most numerous organism on earth, by a long long shot.

By anon36789 — On Jul 14, 2009

what would be the most numerous vertibrate?

Michael Anissimov

Michael Anissimov


Michael Anissimov is a dedicated All The Science contributor and brings his expertise in paleontology, physics, biology...
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