Approximately How Many Species Have Been Identified and Described?

Roughly 1.5 to 2 million species have been formally identified, named, and described by scientists, depending on which catalogue you consult and how you count synonyms. That number sounds enormous until you compare it to the estimated total. A widely cited 2011 analysis predicted around 8.7 million eukaryotic species on Earth, meaning the described fraction would represent only about 14% of what actually exists.¹ Other researchers have argued for a lower total, perhaps 5 million or even under 2 million, but even the most conservative figures leave a yawning gap between what we have catalogued and what remains out there.

Where the 1.5 to 2 Million Figure Comes From

The count of described species is not stored in a single master list everyone agrees on. Multiple databases track species names, and they do not always match. One major global catalogue held over 1.2 million species as of 2011.¹ A separate estimate from 2013 put the number of named species at about 1.5 million.² The gap between those two numbers is partly a timing issue, since thousands of new species are described each year, and partly a bookkeeping problem. Different databases use different naming conventions, carry different numbers of synonyms (two names accidentally assigned to the same organism), and update at different speeds. A study comparing several major name databases found that for butterflies alone, about 15% of names in one database could not be matched to names in another.³ If even a well-studied group like butterflies has that level of mismatch, the uncertainty for less popular organisms is far greater.

How the Count Breaks Down by Group

Animals dominate the described species count, and within animals, insects dominate everything else. About a million insect species have been formally named so far.⁴ That single group accounts for well over half of all known animal species. Beetles make up a huge chunk of that, which inspired the old quip, often attributed to the biologist J.B.S. Haldane, about the Creator having “an inordinate fondness for beetles.” Terrestrial arthropods more broadly, including spiders, mites, and crustaceans, bring the described total to roughly 7 million estimated species, of which only a fraction have been named.

Vertebrates, by contrast, are comparatively well catalogued. A comprehensive dataset of terrestrial vertebrates compiled for research purposes included about 32,900 species: roughly 10,000 reptiles, 10,000 birds, 7,200 amphibians, and 5,700 mammals.⁵ New vertebrate species are still being found, particularly among frogs and lizards in tropical forests, but the overall picture for vertebrates is far more complete than for invertebrates.

Plants add another large slice. The number of known plant species sits at roughly 374,000 to 400,000, depending on whether you include only vascular plants or also mosses, liverworts, and hornworts.⁶ A revised tally put the number of accepted land plant species at about 404,000, with flowering plants accounting for about 369,000 of those.⁷

Fungi are a genuinely enormous kingdom with a small described fraction. About 155,000 fungal species have been formally described, but the actual total could be in the millions.⁸ Many fungi are microscopic, live inside other organisms, or grow in soil and leaf litter where they escape casual notice. Mycologists have long suspected that fungi may rival insects in species richness, though hard numbers remain elusive.

Bacteria, Archaea, and the Microbe Problem

When people quote the 1.5 to 2 million species figure, they are almost always talking about eukaryotes: organisms with complex cells, meaning animals, plants, fungi, and protists. Bacteria and archaea occupy a different and much murkier space. Traditionally, a bacterial “species” needed to be grown in a lab culture and characterized, which left the overwhelming majority of microbes unaccounted for because most refuse to grow in standard lab conditions. A genome-based bacterial and archaeal taxonomy identified about 24,700 species clusters based on DNA sequences, but only around 8,800 of those corresponded to species with formal published names.⁹ Even that figure is a sliver. Environmental DNA studies routinely pull up thousands of distinct microbial lineages from a single scoop of soil or a liter of seawater, many of which have never been seen before. Estimates of total bacterial species range from hundreds of thousands to potentially billions, depending on how finely you draw the lines. The species concept itself was built for sexually reproducing organisms and fits awkwardly on microbes, so any count should be taken as a rough approximation.

Why Total Estimates Vary by Millions

If the described count is uncertain, the estimated total is even more so. The 8.7 million eukaryotic species estimate from 2011 used a statistical pattern in how higher taxonomic ranks (families, orders, classes) relate to the number of species they contain.¹ A competing analysis two years later argued for roughly 5 million total species, with a wide uncertainty range of plus or minus 3 million.² A third approach, based on the rate at which new species are described over time and how that rate might eventually level off, predicted a much lower figure of 1.8 to 2 million species total.¹⁰

These are not just statistical quibbles. The gap between 2 million and 8.7 million is the difference between having described most of life on Earth and having barely scratched the surface. Part of the disagreement hinges on how many insect species exist, since insects are both enormously diverse and poorly surveyed in the tropics. Older estimates from the 1980s, extrapolating from the number of beetle species found on individual tropical trees, suggested there might be 30 million or more arthropod species. More recent and careful analyses have pulled that number down to around 5.5 million insects and 7 million terrestrial arthropods total, with the 30-million figure now considered extremely unlikely.⁴

Another source of disagreement is how you define a species. Researchers who favor a broader species concept (lumping similar populations together) will arrive at a lower total than those who favor a narrower concept (splitting them apart). A perspective piece in the Journal of Biogeography warned that forecasts of undescribed diversity are highly sensitive to whether taxonomists are currently in a “splitting” or “lumping” phase, and that discovery curves alone can badly misjudge the gap if they do not account for ongoing taxonomic revision.¹¹

The Pace of New Descriptions Is Accelerating

One thing nearly all researchers agree on is that the rate of new species descriptions has not slowed down. A 2025 study analyzing historical patterns of species descriptions found that the largest numbers of new species per year have all fallen in the past two decades, roughly 2000 to 2020.¹² Thousands of new species are added to the catalogue every year, from tiny tropical beetles and deep-sea crustaceans to the occasional new frog or primate. In insects, an estimated 80% of species remain undiscovered.⁴

DNA barcoding has played a growing role in that acceleration, particularly by exposing cryptic species, organisms that look identical to the naked eye but turn out to be genetically distinct. A now-classic study found that a single widespread skipper butterfly species in Costa Rica was actually a complex of at least 10 separate species once DNA and natural history observations were combined.¹³ A follow-up study on another neotropical skipper used full nuclear genome sequencing alongside barcoding and morphology to show that what was thought to be one species was actually three, and concluded that cryptic species are a widespread phenomenon in tropical insects.¹⁴ If cryptic species are common across tropical invertebrates, and all evidence suggests they are, the actual species count is higher than what even optimistic morphology-based estimates predict.

Why It Takes So Long to Describe a New Species

Finding a new species and formally describing it are two very different things, and the second step can take years or even decades. A study of frog species descriptions found that the time from collecting the first specimen to publishing a formal description ranged from under a year to over 125 years, with a median of about 7 years.¹⁵ Even more concerning, the time lag is getting longer globally, not shorter. Specimens sit in museum drawers waiting for a specialist who has the time and funding to examine them. Frogs are relatively charismatic and well-studied; for less glamorous organisms like mites, nematodes, or small flies, the wait can be even longer.

The bottleneck is not technology. It is people. The “taxonomic impediment,” as the field calls it, is fundamentally a shortage of trained taxonomists with the institutional support to do the work. A review in the Zoological Journal of the Linnean Society emphasized that fieldwork, specimen collection, and long-term curation of natural history collections remain the rate-limiting steps in describing biodiversity, and that none of these are keeping pace with demand.¹⁶ A study of amphipod crustacean experts highlighted that the problem is compounded by the uneven distribution of specialists around the world: most taxonomists work in wealthy nations, while most undescribed biodiversity lives in the tropics.¹⁷

Geographic Blind Spots

The uneven distribution of taxonomic effort creates serious blind spots in the global species count. Tropical regions contain the highest biodiversity on Earth but have historically received the least scientific attention. A study in Ecuador, one of the most species-rich countries per unit area, found that estimates of total species richness varied wildly depending on how thoroughly an area had been sampled, with limited collecting severely hampering any attempt to estimate the true total from available data.¹⁸ You cannot count what you have never looked for, and for huge swaths of tropical forest, deep ocean floor, and subterranean habitats, the looking has barely begun.

This means the described species count is heavily biased toward certain regions and certain organism types. European birds, North American mammals, and temperate-zone flowering plants are catalogued in fine detail. Tropical soil mites, deep-sea nematodes, and canopy-dwelling beetles in Borneo are not. Any estimate of total species richness has to correct for this uneven effort, and different correction methods yield different answers.

The Hidden Diversity of Parasites

Parasites represent one of the most dramatically undercounted categories of life. Using the largest available database of host-parasite associations and one of the world’s largest parasite collections, researchers estimated that there are roughly 100,000 to 350,000 species of helminth parasites (worms that live inside vertebrates) alone, and that 85 to 95% of them are unknown to science.¹⁹ An earlier estimate for the same group, helminth parasites of vertebrates, arrived at a range of 75,000 to 300,000 species.²⁰

These are not niche organisms of interest only to specialists. Parasites play critical roles in ecosystem function, regulate host populations, and shape the evolution of the animals they inhabit. The fact that the vast majority remain undescribed means we are missing a large piece of how ecosystems work. And helminth worms are just one type of parasite; when you factor in parasitic insects, fungi, protists, and bacteria, the number of undescribed parasitic species grows substantially larger.

Species Going Extinct Before They Are Described

Perhaps the most unsettling dimension of the species-counting problem is that species are disappearing before anyone gets a chance to describe them. This phenomenon, sometimes called “dark extinction,” means the true toll of the current biodiversity crisis is worse than official extinction tallies suggest. For world birds, one of the best-studied groups, statistical methods estimate that about 56 species went extinct unrecorded during the taxonomic period (roughly 1800 to the present) and around 180 during the pre-taxonomic period (1500 to 1800), when European exploration was introducing rats, goats, and other destructive animals to oceanic islands.²¹

For less well-known groups, the proportion of “dark” extinctions is higher. One analysis estimated that the proportion of undiscovered extinct species over all extinctions ranged from 15% to 59%, depending on the organism and region, meaning actual species losses could be up to twice the recorded number.²² Intensive fieldwork in places like Brazil’s Atlantic Forest has turned up species so rare and so threatened that some become extinct within years of being found.²³ The race between describing species and losing them is real, and for many organisms the losing side is ahead.

The Ocean’s Separate Accounting Problem

Marine species present their own counting challenges. The 2011 estimate predicted about 2.2 million eukaryotic species in the ocean, of which roughly 91% await description.¹ The lower-bound estimate disagreed, suggesting marine species make up only about 16% of all species on Earth, with roughly 300,000 total marine species, which would mean a smaller fraction of life lives in the sea than the higher estimates imply.¹⁰ Both sides agree, however, that the ocean harbors greater phylogenetic diversity than land. In other words, while the number of marine species may be lower, the evolutionary breadth of ocean life, from tube worms at hydrothermal vents to gelatinous creatures in the midnight zone, spans more of the tree of life than anything on land. Some marine groups are strikingly well documented for historical reasons. Foraminifera, the tiny shell-building protists whose fossils are invaluable to geologists, have about 54,600 accepted species and infraspecies names in their taxonomic register, most of them described from the fossil record rather than living specimens.²⁴ Others, like the small crustaceans and worms living in deep-sea sediments, remain almost entirely uncharted.

What “Identified and Described” Actually Requires

A species is not officially described just because someone saw it, photographed it, or sequenced its DNA. Formal species description involves collecting a type specimen (a physical example deposited in a museum), publishing a peer-reviewed paper with a diagnosis that distinguishes the new species from its close relatives, and assigning it a binomial Latin name following the rules of the relevant naming code. For animals, those rules are set by the International Code of Zoological Nomenclature; for plants and fungi, by the International Code of Nomenclature for algae, fungi, and plants. The process is deliberate by design, meant to ensure stability and reproducibility. But that deliberateness also creates a backlog. Museums around the world hold millions of specimens that have never been formally studied. Some of those specimens sit in jars of ethanol for decades before a specialist picks them up, and the growing time lag between collection and publication means the backlog is getting worse, not better.¹⁵

DNA-based approaches are speeding up the detection of distinct lineages, but they have not yet replaced the formal description process. A DNA barcode can flag a specimen as likely new, but the naming still requires morphological work, a written diagnosis, and a published paper. Some researchers have proposed streamlined “turbo-taxonomy” pipelines that combine molecular data with rapid morphological characterization, but adoption has been uneven across fields. Whether the formal process will ultimately adapt to the scale of the problem, or whether millions of species will remain unnamed in a limbo of provisional genetic labels, is one of the open questions in biodiversity science.

1
PLoS Biology. How Many Species Are There on Earth and in the Ocean?
2
PubMed. Can we name Earth’s species before they go extinct?
3
Trends in Ecology & Evolution. A globally integrated structure of taxonomy to support biodiversity science and conservation
4
PubMed. How Many Species of Insects and Other Terrestrial Arthropods Are There on Earth?
5
bioRxiv. Shortfalls and opportunities in terrestrial vertebrate species discovery
6
Phytotaxa. The number of known plants species in the world and its annual increase
7
Phytotaxa. Counting counts: revised estimates of numbers of accepted species of flowering plants, seed plants, vascular plants and land plants with a review of other recent estimates
8
PubMed. Fungal diversity, evolution, and classification
9
Nature Biotechnology. A complete domain-to-species taxonomy for Bacteria and Archaea
10
Systematic Biology. Predicting Total Global Species Richness Using Rates of Species Description and Estimates of Taxonomic Effort
11
Journal of Biogeography. How taxonomic change influences forecasts of the Linnean shortfall (and what we can do about it)?
12
PubMed Central. The past and future of known biodiversity: Rates, patterns, and projections of new species over time
13
PubMed Central. Ten species in one: DNA barcoding reveals cryptic species in the neotropical skipper butterfly Astraptes fulgerator
14
PubMed Central. Nuclear genomes distinguish cryptic species suggested by their DNA barcodes and ecology
15
PubMed Central. Croaking for haste: How long does it take to describe a frog species since its discovery?
16
Zoological Journal of the Linnean Society. The taxonomic impediment: a shortage of taxonomists, not the lack of technical approaches
17
Journal of Crustacean Biology. Taxonomy in Times of the Taxonomic Impediment – Examples from the Community of Experts on Amphipod Crustaceans
18
PubMed Central. Limited sampling hampers “big data” estimation of species richness in a tropical biodiversity hotspot
19
Proceedings of the Royal Society B: Biological Sciences. What would it take to describe the global diversity of parasites?
20
PubMed Central. Homage to Linnaeus: How many parasites? How many hosts?
21
PubMed Central. Dark extinction: the problem of unknown historical extinctions
22
PubMed. Estimating how many undescribed species have gone extinct
23
PubMed. Species, extinct before we know them?
24
GeoScienceWorld (Journal of Foraminiferal Research). Foraminifera in the World Register of Marine Species (Worms) Taxonomic Database