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There are approximately 1.25 million identified animal species, but there could be up to 30 million unidentified insect species and 1 million mite species. The number of animal species on Earth is declining due to human-caused events such as the Holocene Extinction Event.
There are approximately 1,250,000 identified animal species. This includes 1,190,200 invertebrates, including 950,000 insects, 70,000 molluscs, 40,000 crustaceans and 130,200 others. There are approximately 58,800 identified vertebrates, including 29,300 fish, 5,743 amphibians, 8,240 reptiles, 9,800 birds, and 5,416 mammals. By way of comparison, nearly 300,000 plant species are known.
Importantly, the numbers above do not account for species that have not yet been caught or scientifically described. Scientists estimate that there could be as many as 10-30 million species of unidentified insects, many of which live in the rainforest, and up to 1 million species of mites. Mites are small arthropods, a group of animals related to, but not the same as, insects.
It is clear that modern science is not aware of all species on the planet. When Carl Linnaeus and his pupils set out to record as many species as they could in the mid-18th century, they found just over 18 species of animals. Today estimates of the total number range from 15,000 to 2 million. In addition to all animals, there are between 30 million and 10 billion species of bacteria and archaea. Furthermore, the number of species today is thought to represent only 1% of all species that ever lived, as mass extinctions in the past probably killed up to 1% of all species.
Unfortunately, the number of animal species on Earth today is declining. An event known as the Holocene Extinction Event, caused by humans, is underway. When humans first spread across the globe, many species went extinct, including all of the Pleistocene megafuna, which were completely wiped out by 9,000 years ago. These include the mammoth, mastodon, aurochs, saber-toothed tiger, cave bear, short-faced bear, dire wolf, camelops, woolly rhinoceros, giant lizards, many marsupials, and others. Today, with booming human populations, global warming, and widespread deforestation and poaching, the destruction of thousands of species continues.
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