We know how many species have been discovered and named, but it is difficult to say exactly how many species exist on Earth. Scientists have been able to describe and record a little over 1.5 million species of plants and animals so far (IUCN, 2004). However, this number does not reflect the total number of species that actually live on Earth.

• Many species are still unknown, especially in the tropical regions. In contrast, temperate regions have been more thoroughly studied, and so the records are more complete there. Since most undiscovered species are expected to be found in the tropics, scientists compare insect species in tropical and temperate areas and use that data to estimate the global number of species.
• Some scientists have estimated that the total number of species could be anywhere between 20 to 50 million. However, a widely accepted and more scientifically sound estimate, proposed by Robert May, places the number of total species on Earth at about 7 million.
• Out of all the species that have been discovered and documented so far, more than 70% are animals, while plants, including algae, fungi, bryophytes, gymnosperms, and angiosperms, make up no more than 22% of the total.
• Among the animals, insects are the most species-rich group, contributing to over 70% of all animal species. In simple terms, this means that out of every 10 animals on Earth, 7 are insects. This reflects the enormous diversification and adaptive success of insects.
• Another interesting observation is that the number of fungi species identified globally is greater than the combined total of species of fishes, amphibians, reptiles, and mammals. This highlights the hidden richness of microbial and non-vascular life forms, which are often less studied but ecologically significant.
• it should be noted that the current estimates of species diversity across the globe do not account for prokaryotes such as bacteria and archaea. Biologists are still uncertain about how many prokaryotic species might exist. One of the main challenges is that conventional taxonomic methods are not suitable for microbial organisms, as many microbes cannot be cultured in laboratory conditions. If biochemical or molecular criteria (such as DNA-based techniques) are used to define species, the number of prokaryotic species alone may run into several millions, indicating that global biodiversity is vastly underestimated.
• Although India occupies only 2.4% of the world’s land area, it holds an impressive 8.1% of the global species diversity, making it one of the 12 mega-diversity countries in the world. So far, nearly 45,000 species of plants and about 90,000 animal species have been recorded in India. However, the actual number of living species is likely much higher. If we apply Robert May’s estimate that only 22% of global species have been described, then India could have over 1,00,000 plant species and more than 3,00,000 animal species that are yet to be discovered and documented.