If you’ve ever walked through a forest or even just scrolled through a nature documentary on Netflix, you’ve probably asked yourself: how many kinds of animals are there in the world? It’s a simple question. Kids ask it all the time. But if you ask a taxonomist—the people whose entire jobs revolve around naming things—they’ll probably just sigh.
The short answer is that we don't really know.
Not even close, actually.
Current estimates usually sit somewhere around 8.7 million species, but that number is basically a very educated guess. Some scientists think it’s closer to 5 million, while others, looking at the sheer volume of insects and microscopic life, think we could be looking at 100 million distinct types of animals. We’ve only actually described and named about 1.5 million of them. That means the vast majority of our neighbors on this planet are complete strangers to us. It’s a bit humbling, isn't it?
The 8.7 Million Number: Where Does it Come From?
In 2011, a landmark study published in PLOS Biology by Camilo Mora and his team at Dalhousie University made waves. They didn't go out and count every beetle in the Amazon. Instead, they used math. By looking at the patterns in how we categorize life—groups, families, orders—they projected the total number.
They estimated about 7.77 million species of animals, with the rest of the 8.7 million being fungi, plants, and protozoa.
But science isn't a stagnant pool. It moves. Since that study, other researchers have pointed out that we might be missing the mark on insects. If you think about the fact that almost every species of tropical tree might host a unique species of beetle, the numbers start to explode. Terry Erwin, a famous entomologist, once famously estimated there could be 30 million species of insects alone just by fogging trees in Panama and seeing what fell out.
Why the Count is Always Wrong
Taxonomy is messy. Nature doesn't like boxes.
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One of the biggest hurdles in answering how many kinds of animals are there in the world is the definition of a "species." Traditionally, we say if two animals can breed and produce fertile offspring, they're the same species. But then you have hybrids. You have asexual reproduction. You have "cryptic species"—animals that look identical to our eyes but have DNA so different they haven't interbred for a million years.
The Hidden Giants of the Deep
We know more about the surface of the Moon than we do about the bottom of the ocean. Seriously.
The deep sea is a massive, pressurized warehouse of the unknown. Every time a remote-operated vehicle (ROV) goes down into the Mariana Trench or explores a hydrothermal vent, it finds something weird. Often, it finds dozens of things weird. Most of these deep-sea critters are invertebrates—squishy, glowing, or armored things that don't fit into our backyard categories of "bird" or "dog."
The Insect Empire
If you want to talk about numbers, you have to talk about bugs.
Insects make up the lion's share of animal diversity. There are roughly 1 million described insect species, but experts like those at the Smithsonian Institution suggest there are likely several million more waiting for a name. Beetles alone (Coleoptera) account for about 40% of all known insect species. As the geneticist J.B.S. Haldane reportedly joked, if a Creator exists, He must have an "inordinate fondness for beetles."
Breaking Down the Known Groups
When we talk about "kinds" of animals, most people think of vertebrates. Mammals, birds, reptiles. But in the grand scheme of things, vertebrates are a tiny, vocal minority. They’re the 1% of the animal kingdom.
- Invertebrates: Roughly 97% of all animal species. This includes everything from the dust mites in your carpet to the giant squid. Spiders, worms, jellyfish, crabs—these are the real owners of the planet.
- Fish: There are about 34,000 known species of fish. That’s more than all mammals, birds, reptiles, and amphibians combined.
- Birds: We’ve got about 10,000 to 11,000 species here. This is one of the groups we actually know pretty well because birds are easy to see and hear.
- Mammals: The group we belong to is surprisingly small. There are only about 6,400 species of mammals. Think about that. There are more types of ants in a single hectare of rainforest than there are types of mammals on the entire Earth.
- Reptiles and Amphibians: We're looking at roughly 11,000 reptiles and 8,000 amphibians. These numbers are growing quickly as DNA sequencing reveals that what we thought was one type of frog is actually five different ones.
The Race Against Time
Here is the heartbreaking part of the "how many kinds of animals are there in the world" puzzle: we are losing them faster than we can find them.
Conservationists call this the "Sixth Mass Extinction." Because of habitat loss, climate change, and pollution, species are blinking out of existence before a scientist ever gets a chance to put a Latin name on them. It’s like a library burning down before anyone has even read the books.
Researchers like E.O. Wilson, the legendary biologist, spent decades pushing for a global biodiversity survey. The goal isn't just to satisfy curiosity. It's about ecosystem services. We don't know which obscure fly or soil worm holds the key to a new medicine or keeps a specific food crop from failing.
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DNA Barcoding: The New Frontier
The old way of identifying animals involved looking at them through a microscope and counting the hairs on a leg. It takes forever. It’s prone to human error.
Enter DNA barcoding.
By looking at a specific, short section of mitochondrial DNA, scientists can now identify a species almost like a grocery store scanner reads a UPC. Projects like the International Barcode of Life (iBOL) are trying to build a digital library of all eukaryotic life. This technology is revealing that the world is much more crowded than we thought. In some cases, a single "kind" of stinging wasp has been revealed to be a complex of 10 or 15 different species that just happen to look the same.
Finding New Animals in Your Backyard
You don't have to go to the Congo or the Amazon to find new kinds of animals.
New species are discovered in urban areas all the time. In 2014, a new species of leopard frog (Rana kauffeldi) was discovered in New York City. It had been living there the whole time, right under the noses of millions of people, but everyone just assumed it was a regular bullfrog or southern leopard frog. Its unique "chuck" sound gave it away.
Basically, the world is still a very mysterious place.
How to Help Document Biodiversity
If you’re fascinated by the question of how many kinds of animals are there in the world, you can actually contribute to the answer. You don't need a PhD. You just need a smartphone and some curiosity.
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- Use iNaturalist: This app is a game-changer. You take a photo of an insect, bird, or lizard, and the community (and AI) helps identify it. Your data points are used by real scientists to track migrations and species ranges.
- Support Taxonomy: Funding for "old-fashioned" biology is drying up in favor of high-tech lab work. Supporting natural history museums and universities that maintain biological collections is vital.
- Citizen Science Projects: Look for local bioblitzes. These are 24-hour events where people try to find and identify as many species as possible in a specific area.
The total count of animal species is a moving target. We might never have a final, perfect number, and honestly, that’s okay. The fact that there are millions of living things still waiting to be met is what makes biology the most exciting field on Earth.
To stay informed and contribute to the global count, start documenting the wildlife in your own neighborhood. Every observation helps fill in the gaps of our planetary map. Focus on protecting local habitats, as even a small backyard pond can host species that are part of the millions we are still trying to understand.