How Many Species of Animals Are There in the World?

It is impossible to determine how many individual animals there are at any given point. In the time it took to read that sentence, many hundreds of millions of animals were born and died. Some animal species may have many millions of individuals, others only a relative few.

According to the International Union for Conservation of Nature (IUCN), it was considered there were around 1,565,855 species of animals worldwide in the year 2024^[1]. Below, we look at the total amount of each animal according to type:

• Mammals: 6,736
• Birds: 11,195
• Reptiles: 12,263
• Amphibians: 8,776
• Arachnids: 95,966
• Corals: 5,641
• Crustaceans: 90,820
• Fish: 36,953
• Insects: 1,053,578
• Mollusks: 87,254
• Other invertebrates: 156,447

Also according to the IUCN), approximately 2.13 million total animal species have been recorded as of 2021. These numbers only represent only a fraction of the actual biodiversity. The total number of species is estimated to be between 5 and 10 million. If we include microscopic organisms such as bacteria, the numbers could reach billions. It is worth noting that Wiens (2021) mentions that estimates of the actual number (both described and undescribed) have varied from a few million to trillions^[2].

You can learn more about how life on Earth is classified with our article asking what makes an animal?

The IUCN has documented more than 46,300 species threatened with extinction. This represents approximately 28% of all species that have been assessed. This is because the Earth is currently facing its sixth mass extinction event, where an estimated one million species could disappear in the coming decades. Of the total animals classified as endangered, 27% are mammals, 41% amphibians, 37% sharks and rays, and 21% reptiles.

Human activity is the main cause of this crisis. Factors such as habitat destruction, overexploitation of resources, pollution and climate change contributing significantly to biodiversity loss. Species such as the Gran Canaria giant lizard (Gallotia stehlini) and the Borneo elephant (Elephas maximus borneensis) have experienced drastic declines in their populations. Others have improved their status thanks to conservation effotys, as is the case with the Iberian lynx (Lynx pardinus).

Climate change also poses a serious threat to biodiversity. It is estimated that up to 35% of animal species could become extinct in the wild by 2050 if greenhouse gas emissions continue to rise. Reducing these gases will be crucial to preserving wildlife on our planet.

Learn about one animal whose population numbers will never recover with our article asking why did the great auk go extinct?

The diversity of animal species in the world is a complex and constantly area of study. Although scientists have described and catalogued many millions of existing species, it is estimated that only a small part of global biodiversity is known. In total, only between 1.5 and 2 million species have been discovered so far.

The impossibility of accurately counting all species is due to several factors. This includes the extinction of many animals before they can be identified. We are still discovering many prehistoric animals such as dinosaurs thanks to new additions to the fossil record. Taxonomic classification was pioneered by Carl von Linné in the 18th century. While it remains fundamental, current science faces significant challenges in identifying new species.

The use of modern techniques, such as environmental DNA sequencing, allows organisms to be identified from their genetic fingerprints in the environment. This facilitates the detection of unknown species. Extrapolation of data from known taxonomic groups also provides estimates of total biodiversity. The International Union for Conservation of Nature (IUCN) updates the species register annually, but the list remains incomplete.

Using these data garnered from various techniques, estimates of the total number of species are often made by comparing well-studied groups with lesser known species. Such extrapolation allows scientists to make inferences about the number of species that have yet to be discovered.

One of the main obstacles that scientists face in counting animal species is the vastness of unexplored habitats, especially in hard-to-reach regions such as tropical forests and the deep ocean. Microscopic organisms also present an additional challenge. Their rapid mutation and reproduction complicate their classification and estimation of population numbers.

The evolutionary process of speciation is what leads to animals becoming a distinct species when compared to others. This is another important aspect when trying to determine how many animal species there are in the world. This process can occur when populations of the same species become geographically isolated, allowing for divergent evolution.

Learn more about the complicated process of speciation with our articles asking what is rapid evolution and what is parallel evolution in biology?

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